OpenCores
URL https://opencores.org/ocsvn/socgen/socgen/trunk

Subversion Repositories socgen

[/] [socgen/] [trunk/] [Projects/] [opencores.org/] [logic/] [ip/] [ps2_interface/] [doc/] [ref/] [The_PS_2_Keyboard_Interface.html] - Blame information for rev 131

Details | Compare with Previous | View Log

Line No. Rev Author Line
1 131 jt_eaton 
<!DOCTYPE doctype PUBLIC "-//w3c//dtd html 4.0 transitional//en">
2 
<html><head>
3 
 
4 
 
5 
 
6 
 
7 
  <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
8 
 
9 
  <meta name="GENERATOR" content="Mozilla/4.76 [en] (Win98; U) [Netscape]">
10 
 
11 
  <meta name="Author" content="Adam Chapweske">
12 
  <title>The PS/2 Keyboard Interface</title>
13 
                                     <!--This file created 10:20 PM  3/29/01 by Claris Home Page version 3.0-->
14 
 
15 
  <meta name="author" content="Adam Chapweske">
16 
</head><body vlink="#3333ff" alink="#3333ff" bgcolor="#ffffff" link="#3333ff">
17 
   <small><b><font face="Arial,Helvetica"><font size="+3"><small>The PS/2
18 
Keyboard  Interface</small></font></font></b></small><br>
19 
 
20 
 
21 
<center></center>
22 
 
23 
<center>
24 
<hr size="1" width="400" align="left" noshade="noshade"></center>
25 
                <br>
26 
   <font face="Arial,Helvetica">Source: <a href="http://www.computer-engineering.org/">http://www.Computer-Engineering.org</a></font><br>
27 
    <font face="Arial,Helvetica">Author: Adam Chapweske<br>
28 
   Last Updated: 04/01/03<br>
29 
 
30 
   <br>
31 
   </font><b>Legal Information:</b><br>
32 
     <br>
33 
     All information within this article is provided "as is" and without
34 
any   express or implied warranties, including, without limitation, the implied
35 
  warranties of merchantibility and fitness for a particular purpose. &nbsp;<br>
36 
    <br>
37 
    This article is protected under copyright law. &nbsp;This document may
38 
 be  copied only if the source, author, date, and legal information is included.<br>
39 
   <br>
40 
 
41 
   <b>Abstract:</b><br>
42 
   <br>
43 
   This article tries to cover every aspect of AT and PS/2 keyboards.&nbsp;
44 
    It includes information on the low-level signals and protocol, scan codes,
45 
    the command set, initialization, compatibility issues, and other miscellaneous
46 
    information.&nbsp; Since it's closely related, I've also included information
47 
    on the PC keyboard controller.&nbsp; All code samples involving the keyboard
48 
  encoder are written in assembly for <a href="http://www.microchip.com/">Microchip's</a>
49 
  PIC microcontrollers.&nbsp;   All code samples related to the keyboard
50 
controller   are written in x86 assembly<br>
51 
 
52 
 
53 
<p><b>A History Lesson:</b> </p>
54 
 
55 
<p>The most popular keyboards in use today include: </p>
56 
 
57 
<ul>
58 
     <li> USB keyboard - Latest keyboard supported by all new computers (Macintosh
59 
    and IBM/compatible).&nbsp; These are relatively complicated to interface
60 
   and are not covered in this article.</li>
61 
     <li> IBM/Compatible keyboards - Also known as "AT keyboards" or "PS/2
62 
   keyboards",  all modern PCs support this device.&nbsp; They're the easiest
63 
   to interface,  and are the subject of this article.</li>
64 
 
65 
     <li> ADB keyboards - Connect to the Apple Desktop Bus of older Macintosh
66 
    systems.&nbsp; These are not covered in this article&nbsp;</li>
67 
 
68 
</ul>
69 
         IBM introduced a new keyboard with each of its major desktop computer
70 
   models.&nbsp;  The original IBM PC, and later the IBM XT, used what we
71 
call   the "XT keyboard."&nbsp;  These are obsolete and differ significantly
72 
from   modern keyboards; the XT  keyboard is not covered in this article.&nbsp;
73 
  Next came the IBM AT system  and later the IBM PS/2.&nbsp; They introduced
74 
  the keyboards we use today,  and are the topic of this article.&nbsp; AT
75 
 keyboards and PS/2 keyboards were very similar devices, but the PS/2 device
76 
 used a smaller connector and supported a few additional features.&nbsp;
77 
 
78 
Nonetheless,    it remained backward compatible with AT systems and few of
79 
the additional    features ever caught on (since software also wanted to
80 
remain backward compatible.)&nbsp;   Below is a summary of IBM's three major
81 
keyboards.
82 
<p>IBM PC/XT Keyboard (1981): </p>
83 
 
84 
<ul>
85 
     <li> 83 keys</li>
86 
     <li> 5-pin DIN connector</li>
87 
     <li> Simple uni-directional serial protocol</li>
88 
 
89 
     <li> Uses what we now refer to as scan code set 1</li>
90 
     <li> No host-to-keyboard commands</li>
91 
 
92 
</ul>
93 
         IBM AT Keyboard (1984) - Not backward compatible with XT systems<tt><a href="#A%20History%20Lesson%20FN">(1)</a></tt>.
94 
 
95 
<ul>
96 
     <li> 84 -101 keys</li>
97 
 
98 
     <li> 5-pin DIN connector</li>
99 
     <li> Bi-directional serial protocol</li>
100 
     <li> Uses what we now refer to as scan code set 2</li>
101 
     <li> Eight host-to-keyboard commands</li>
102 
 
103 
 
104 
</ul>
105 
         IBM PS/2 Keyboard (1987) - Compatible with AT systems, not compatible
106 
   with  XT systems<tt><a href="#A%20History%20Lesson%20FN">(1)</a></tt>.
107 
 
108 
<ul>
109 
     <li> 84 - 101 keys</li>
110 
     <li> 6-pin mini-DIN connector</li>
111 
     <li> Bi-direction serial protocol</li>
112 
 
113 
     <li> Offers optional scan code set 3</li>
114 
     <li> 17 host-to-keyboard commands&nbsp;</li>
115 
 
116 
</ul>
117 
         The PS/2 keyboard was originally an extension of the AT device.&nbsp;
118 
   It  supported a few additional host-to-keyboard commands and featured
119 
a  smaller   connector.&nbsp; These were the only differences between the
120 
two  devices.&nbsp;   However, computer hardware has never been about standards
121 
 as much as compatibility.&nbsp;   For this reason, any keyboard you buy
122 
today  will be <i>compatible</i> with   PS/2 and AT systems, but it may not
123 
fully  support all the features of the   original devices.
124 
 
125 
 
126 
<p>Today, "AT keyboard" and "PS/2 keyboard" refers only to their connector
127 
    size.&nbsp; Which settings/commands any given keyboard does or does not
128 
  support is anyone's guess.&nbsp; For example, the keyboard I'm using right
129 
  now has a PS/2-style connector but only fully supports seven commands, partially
130 
   supports two, and merely "acknowledges" the rest.&nbsp; In contrast, my
131 
 "Test"  keyboard has an AT-style connector but supports every feature/command
132 
  of the original PS/2 device (plus a few extra.)&nbsp; It's important you
133 
 treat modern keyboards as compatible, not standard.&nbsp; If your design
134 
a keyboard-related device that relies on non-general features, it may work
135 
on some systems, but not on others...         </p>
136 
 
137 
<p>Modern PS/2 (AT) compatible keyboards </p>
138 
 
139 
<ul>
140 
 
141 
     <li> Any number of keys (usually 101 or 104)</li>
142 
     <li> 5-pin or 6-pin connector; adaptor usually included</li>
143 
     <li> Bi-directional serial protocol</li>
144 
     <li> Only scan code set 2 guaranteed.</li>
145 
     <li> Acknowledges all commands; may not act on all of them.</li>
146 
 
147 
 
148 
</ul>
149 
         <a name="A History Lesson FN"></a> <br>
150 
              <i>Footnote 1) XT keyboards use a completely different protocol
151 
  than   that used by AT and PS/2 systems, making it incompatible with the
152 
 newer PCs.&nbsp; However, there was a transition period where some keyboard
153 
 controllers supported both XT and AT (PS/2) keyboards (through a switch,
154 
jumper, or auto-sense.)&nbsp;   Also, some keyboards were made to work on
155 
both types of systems (again, through the use of a switch or auto-sensing.)&nbsp;
156 
If you've owned such a PC or keyboard, don't let it fool you--XT keyboards
157 
are NOT compatible with modern computers.</i>
158 
 
159 
<p><b>General Description:</b> </p>
160 
 
161 
 
162 
<p>Keyboards consist of a large matrix of keys, all of which are monitored
163 
    by an on-board processor (called the "keyboard encoder".)&nbsp; The specific
164 
    processor<tt><a href="#General%20Description%20FN">(1)</a></tt> varies
165 
 from   keyboard-to-keyboard but they all basically do the same thing:&nbsp;
166 
 Monitor   which key(s) are being pressed/released and send the appropriate
167 
 data to  the host.&nbsp; This processor takes care of all the debouncing
168 
and buffers  any data in its 16-byte buffer, if needed.&nbsp; Your motherboard
169 
 contains  a "keyboard controller"<tt><a href="#General%20Description%20FN">(2)</a></tt>   that is in charge of decoding
170 
 all of the data received from the keyboard  and informing your software of
171 
 what's going on.&nbsp; All communication between  the host and the keyboard
172 
 uses an IBM protocol.&nbsp; <br>
173 
 
174 
              <a name="General Description FN"></a> <br>
175 
              <i>Footnote 1)&nbsp; Originally, IBM used the Intel 8048 microcontroller
176 
    as its keyboard encoder. &nbsp;There are now a wide variety of keyboard
177 
   encoder chips available from many different manufacturers.</i> </p>
178 
                                                <i>Footnote 2) Originally,
179 
 IBM used the Intel 8042 microcontroller as  its  keyboard controller.&nbsp;
180 
 This has since been replaces with compatible   devices integrated in motherboards'
181 
 chipsets. The keyboard controller is  covered later in this article.</i>
182 
 
183 
<p><b>Electrical Interface / Protocol:</b> </p>
184 
 
185 
 
186 
<p>The AT and PS/2 keyboards use the same protocol as the PS/2 mouse.&nbsp;
187 
    Click <a href="http://www.computer-engineering.org/ps2protocol">here</a>   for detailed information on
188 
 this protocol. </p>
189 
 
190 
<p><b>Scan Codes:</b> </p>
191 
 
192 
<p>Your keyboard's processor spends most of its time "scanning", or   monitoring,
193 
 the matrix of keys.&nbsp; If it finds that any key is being pressed,  released,
194 
 or held down, the keyboard will send a packet of information known  as a
195 
"scan code" to your computer.&nbsp; There are two different types of  scan
196 
codes: "make codes"<i> </i>and "break codes".&nbsp; A make code is sent  when
197 
a key is pressed or held down.&nbsp; A break code is sent when  a key  is
198 
released.&nbsp; Every key is assigned its own unique make code and break
199 
code so the host can determine exactly what happened to which key by looking
200 
 at a single scan code.&nbsp; The set of make and break codes for every key
201 
 comprises a "scan code set".&nbsp; There are three standard scan code sets,
202 
 named one, two, and three.&nbsp; All modern keyboards default  to set two.<tt><a href="#Scancodes%20FN">(1)</a></tt> </p>
203 
 
204 
 
205 
<p>So how do you figure out what the scan codes are for each key?&nbsp;
206 
  Unfortunately, there's no simple formula for calculating this.&nbsp; If
207 
  you want to know what the make code or break code is for a specific key,
208 
 you'll have to look it up in a table.&nbsp; I've composed tables for all
209 
make codes and break codes in all three scan code sets: </p>
210 
 
211 
<ul>
212 
     <li> <a href="http://www.computer-engineering.org/ps2keyboard/scancodes1.html">Scan   Code Set 1</a> - Original XT scan
213 
  code set; supported by some modern keyboards</li>
214 
 
215 
     <li> <a href="http://www.computer-engineering.org/ps2keyboard/scancodes2.html">Scan   Code Set 2</a> - Default scan
216 
code  set for all modern keyboards</li>
217 
     <li> <a href="http://www.computer-engineering.org/ps2keyboard/scancodes3.html">Scan   Code Set 3</a> - Optional PS/2
218 
scan  code set--rarely used</li>
219 
 
220 
</ul>
221 
         <a name="Scancodes FN"></a> <br>
222 
 
223 
              <i>Footnote 1) Originally, the AT keyboard only supported set
224 
 two,   and the PS/2 keyboard would default to set two but supported all three.&nbsp;
225 
    Most modern keyboards behave like the PS/2 device, but I have come across
226 
    a few that didn't support set one, set three, or both.&nbsp; Also, if
227 
you've    ever done any low-level PC programming, you've probably notice
228 
the keyboard    controller supplies set ONE scan codes by default.&nbsp; This
229 
is because   the keyboard controller converts all incomming scan codes to
230 
set one (this   stems from retaining compatibility with software written for
231 
XT systems.)&nbsp;    However, it's still set two scan codes being sent down
232 
the keyboard's serial    line.&nbsp;</i>
233 
 
234 
<p><b>Make Codes, Break Codes, and Typematic Repeat:</b> </p>
235 
 
236 
<p>Whenever a key is pressed, that key's make code is sent to the computer.&nbsp;
237 
    Keep in mind that a make code only represents a <u>key</u> on a keyboard--it
238 
    does not represent the character printed on that key.&nbsp; This means
239 
 that  there is no defined relationship between a make code and an ASCII code.&nbsp;
240 
 
241 
   It's up to the host&nbsp; to translate scan codes to characters or commands.
242 
          </p>
243 
 
244 
<p>Although most set two make codes are only one-byte wide, there are   a
245 
 handfull of "extended keys" whose make codes are two or four bytes wide.&nbsp;
246 
    These make codes can be identified by the fact that their first byte is
247 
  E0h.&nbsp;        </p>
248 
 
249 
<p>Just as a make code is sent to the computer whenever a key is pressed,
250 
    a break code is sent whenever a key is released.&nbsp; In addition to
251 
every    key having its own unique make code, they all have their own unique
252 
break    code<tt><a href="#MakeBreakTypematic%20FN">(1)</a></tt>.&nbsp; Fortunately,
253 
    however, you won't always have to use lookup tables to figure out a key's
254 
    break code--certain relationships do exist between make codes and break
255 
  codes.&nbsp; Most set two break codes are two bytes long where the first
256 
 byte is F0h and the second byte is the make code for that key.&nbsp; Break
257 
 codes for extended keys are usually three bytes long where the first two
258 
bytes are E0h, F0h, and the last byte is the last byte of that key's make
259 
code.&nbsp; As an example, I have listed below a the set two make codes and
260 
break codes for a few keys:&nbsp;        </p>
261 
 
262 
 
263 
<blockquote>
264 
  <blockquote>
265 
 
266 
    <blockquote>&nbsp;
267 
 
268 
      <table width="300" border="1" cols="3">
269 
         <tbody>
270 
                        <tr>
271 
         <td>
272 
 
273 
 
274 
            <center>Key</center>
275 
         </td>
276 
          <td>
277 
 
278 
 
279 
            <center>(Set 2) <br>
280 
 
281 
        Make Code</center>
282 
         </td>
283 
          <td>
284 
 
285 
 
286 
            <center>(Set 2) <br>
287 
        Break Code</center>
288 
         </td>
289 
         </tr>
290 
          <tr>
291 
 
292 
         <td>
293 
 
294 
 
295 
            <center>"A"</center>
296 
         </td>
297 
          <td>
298 
 
299 
 
300 
            <center>1C</center>
301 
         </td>
302 
          <td>
303 
 
304 
 
305 
            <center>F0,1C</center>
306 
         </td>
307 
 
308 
         </tr>
309 
          <tr>
310 
         <td>
311 
 
312 
 
313 
            <center>"5"</center>
314 
         </td>
315 
          <td>
316 
 
317 
 
318 
            <center>2E</center>
319 
         </td>
320 
          <td>
321 
 
322 
 
323 
            <center>F0,2E</center>
324 
 
325 
         </td>
326 
         </tr>
327 
          <tr>
328 
         <td>
329 
 
330 
 
331 
            <center>"F10"</center>
332 
         </td>
333 
          <td>
334 
 
335 
 
336 
            <center>09</center>
337 
         </td>
338 
 
339 
          <td>
340 
 
341 
 
342 
            <center>F0,09</center>
343 
         </td>
344 
         </tr>
345 
          <tr>
346 
         <td>
347 
 
348 
 
349 
            <center>Right Arrow</center>
350 
         </td>
351 
          <td>
352 
 
353 
 
354 
            <center>E0, 74</center>
355 
 
356 
         </td>
357 
          <td>
358 
 
359 
 
360 
            <center>E0, F0, 74</center>
361 
         </td>
362 
         </tr>
363 
          <tr>
364 
         <td>
365 
 
366 
 
367 
            <center>Right "Ctrl"</center>
368 
         </td>
369 
 
370 
          <td>
371 
 
372 
 
373 
            <center>E0, 14</center>
374 
         </td>
375 
          <td>
376 
 
377 
 
378 
            <center>E0, F0, 14</center>
379 
         </td>
380 
         </tr>
381 
 
382 
 
383 
        </tbody>
384 
 
385 
      </table>
386 
 
387 
         </blockquote>
388 
         </blockquote>
389 
         Example:&nbsp; What sequence of make codes and break codes should
390 
 be  sent   to your computer for the character "G" to appear in a word processor?&nbsp;
391 
    Since this is an upper-case letter, the sequence of events that need to
392 
  take place are: press the "Shift" key, press the "G" key, release the "G"
393 
  key, release the "Shift" key.&nbsp; The scan codes associated with these
394 
 events are the following:&nbsp; make code for the "Shift" key (12h), make
395 
 code for the "G" key (34h), break code for the "G" key(F0h,34h), break code
396 
 for the "Shift" key (F0h,12h).&nbsp; Therefore, the data sent to your computer
397 
 would be: 12h, 34h, F0h, 34h, F0h, 12h.</blockquote>
398 
 
399 
         If you press a key, its make code is sent to the computer.&nbsp;
400 
When   you  press and hold down a key, that key becomes <i>typematic</i>,
401 
which  means  the keyboard will keep sending that key's make code until the
402 
key is released  or another key is pressed.&nbsp; To verify this, open a text
403 
editor and hold down the "A" key.&nbsp; When you first press the key, the
404 
character "a" immediately appears on your screen.&nbsp; After a short delay,
405 
another "a" will appear followed by a whole stream of "a"s until you release
406 
the "A" key.&nbsp; There are two important parameters here:&nbsp; the <i>typematic
407 
   delay</i>, which is the short delay between the first and second "a",
408 
and    the <i>typematic rate</i>, which is how many characters per second
409 
will  appear  on your screen after the typematic delay.&nbsp; The typematic
410 
delay  can range  from 0.25 seconds to 1.00 second and the typematic rate
411 
can range  from 2.0  cps (characters per second) to 30.0 cps.&nbsp; You may
412 
change the  typematic  rate and delay using the "Set Typematic Rate/Delay"
413 
(0xF3) command.
414 
 
415 
<p>Typematic data is not buffered within the keyboard.&nbsp; In the   case
416 
 where more than one key is held down, only the last key pressed becomes
417 
  typematic.&nbsp; Typematic repeat then stops when that key is released,
418 
  even though other keys may be held down.  </p>
419 
 
420 
<p><a name="MakeBreakTypematic FN"></a> <br>
421 
              <i>Footnote 1) Actually, the "Pause/Break" key does not have
422 
 a  break   code in scan code sets one and two.&nbsp; When this key is pressed,
423 
  its make code is sent; when it's released, it doesn't send anything. &nbsp;So
424 
  how do you tell when this key has been released? &nbsp;You can't.</i> </p>
425 
 
426 
 
427 
<p><b>Reset:</b> </p>
428 
 
429 
<p>At power-on or software reset (see the "Reset" command) the keyboard
430 
  performs a diagnostic self-test referred to as BAT (Basic Assurance Test)
431 
    and loads the following default values:&nbsp; </p>
432 
 
433 
<ul>
434 
     <li> Typematic delay 500 ms.</li>
435 
     <li> Typematic rate 10.9 cps.</li>
436 
 
437 
     <li> Scan code set 2.</li>
438 
     <li> Set all keys typematic/make/break.</li>
439 
 
440 
</ul>
441 
 
442 
<p>When entering BAT, the keyboard enables its three LED indicators,   and
443 
 turns them off when BAT has completed.&nbsp; At this time, a BAT completion
444 
    code of either 0xAA (BAT successful) or 0xFC (Error) is sent to the host.
445 
  &nbsp; This BAT completion code must be sent 500~750 milliseconds after
446 
power-on.          </p>
447 
 
448 
 
449 
<p>Many of the keyboards I've tested ignore their CLOCK and DATA lines   until
450 
<i>after</i>  the BAT completion code has been sent.&nbsp; Therefore,   an
451 
"Inhibit" condition  (CLOCK line low) may not prevent the keyboard from
452 
 sending its BAT completion  code. </p>
453 
 
454 
<p><b>Command Set:</b> </p>
455 
 
456 
<p>A few notes regarding commands the host can issue to the keyboard:<br>
457 
           </p>
458 
 
459 
 
460 
<ul>
461 
     <li>The keyboard clears its output buffer when it recieves any command.</li>
462 
     <li>If the keyboard receives an invalid command or argument, it must
463 
respond  with "resend" (0xFE).</li>
464 
     <li>The keyboard must not send any scancodes while processing a command.</li>
465 
     <li>If the keyboard is waiting for an argument byte and it instead
466 
receives  a command, it should discard the previous command and process this
467 
 new one.</li>
468 
 
469 
</ul>
470 
     Below are all the commands the host may send to the keyboard:<br>
471 
 
472 
 
473 
<ul>
474 
     <li> 0xFF (Reset) - Keyboard responds with "ack" (0xFA), then enters
475 
 "Reset"  mode.&nbsp; (See "Reset"  section.)</li>
476 
     <li> 0xFE (Resend) - Keyboard responds by resending the last-sent byte.
477 
   &nbsp;The exception to this is if the last-sent byte was "resend" (0xFE).
478 
   &nbsp;If this is the case, the keyboard resends the last non-0xFE byte.
479 
 &nbsp;This  command is used by the host to indicate an error in reception.</li>
480 
 
481 
</ul>
482 
 
483 
 
484 
<blockquote>The next six commands can be issued when the keyboard is  in any
485 
mode, but it only effects the behavior of the keyboard when in "mode  3"
486 
(ie, set to scan code set 3.) <br>
487 
             </blockquote>
488 
 
489 
<ul>
490 
     <li> *0xFD (Set Key Type Make) - Disable break codes and typematic repeat
491 
 for specified keys. &nbsp;Keyboard responds with "ack" (0xFA), then disables
492 
 scanning (if enabled) and reads a list of keys from the host. &nbsp;These
493 
  keys are specified by their set 3 make codes. &nbsp;Keyboard responds to
494 
 each make code with "ack". &nbsp;Host terminates this list by sending an
495 
invalid set 3 make code (eg, a valid command.) &nbsp;The keyboard then re-enables
496 
  scanning (if previously disabled).</li>
497 
     <li> *0xFC (Set Key Type Make/Break) - Similar to previous command,
498 
 except  this one only disables typematic repeat.</li>
499 
 
500 
     <li> *0xFB (Set Key Type Typematic) - Similar to previous two, except
501 
  this one only disables break codes.</li>
502 
     <li> *0xFA (Set All Keys Typematic/Make/Break) - Keyboard responds with
503 
 "ack" (0xFA). &nbsp;Sets all keys to their normal setting (generate scan
504 
codes on make, break, and typematic repeat)</li>
505 
     <li> *0xF9 (Set All Keys Make) - Keyboard responds with "ack" (0xFA).
506 
  &nbsp;Similar to 0xFD, except applies to all keys.</li>
507 
     <li> *0xF8 (Set All Keys Make/Break) - Keyboard responds with "ack"
508 
 (0xFA).  &nbsp;Similar to 0xFC, except applies to all keys.</li>
509 
 
510 
     <li> *0xF7 (Set All Keys Typematic) - Keyboard responds with "ack" (0xFA).
511 
  &nbsp;Similar to 0xFB, except applies to all keys.</li>
512 
     <li> 0xF6 (Set Default) - Load default typematic rate/delay (10.9cps
513 
 /  500ms), key types (all keys typematic/make/break), and scan code set (2).</li>
514 
     <li> 0xF5 (Disable) - Keyboard stops scanning, loads default values
515 
 (see   "Set Default" command), and waits further instructions.</li>
516 
     <li> 0xF4 (Enable) - Re-enables keyboard after disabled using previous
517 
   command.</li>
518 
 
519 
     <li> 0xF3 (Set Typematic Rate/Delay) - Host follows this command with
520 
   one argument byte that defines the typematic rate and delay as follows:</li>
521 
     <br>
522 
        .
523 
  <center><b>Repeat Rate</b></center>
524 
 
525 
  <center>
526 
  <table width="90%" border="1" cellpadding="0" cellspacing="0">
527 
         <tbody>
528 
                    <tr>
529 
 
530 
         <td>
531 
 
532 
        <center>Bits 0-4</center>
533 
         </td>
534 
          <td>
535 
 
536 
        <center>Rate(cps)</center>
537 
         </td>
538 
          <td bgcolor="#cccccc">&nbsp;</td>
539 
          <td>
540 
 
541 
        <center>Bits 0-4</center>
542 
 
543 
         </td>
544 
          <td>
545 
 
546 
        <center>Rate(cps)</center>
547 
         </td>
548 
          <td bgcolor="#cccccc">&nbsp;</td>
549 
          <td>
550 
 
551 
        <center>Bits 0-4</center>
552 
         </td>
553 
          <td>
554 
 
555 
        <center>Rate(cps)</center>
556 
 
557 
         </td>
558 
          <td bgcolor="#cccccc">&nbsp;</td>
559 
          <td>
560 
 
561 
        <center>Bits 0-4</center>
562 
         </td>
563 
          <td>
564 
 
565 
        <center>Rate(cps)</center>
566 
         </td>
567 
         </tr>
568 
 
569 
          <tr>
570 
         <td>
571 
 
572 
        <center><tt>00h</tt></center>
573 
         </td>
574 
          <td>
575 
 
576 
        <center><tt>30.0</tt></center>
577 
         </td>
578 
          <td bgcolor="#cccccc">&nbsp;</td>
579 
          <td>
580 
 
581 
        <center><tt>08h</tt></center>
582 
 
583 
         </td>
584 
          <td>
585 
 
586 
        <center><tt>15.0</tt></center>
587 
         </td>
588 
          <td bgcolor="#cccccc">&nbsp;</td>
589 
          <td>
590 
 
591 
        <center><tt>10h</tt></center>
592 
         </td>
593 
          <td>
594 
 
595 
        <center><tt>7.5</tt></center>
596 
 
597 
         </td>
598 
          <td bgcolor="#cccccc">&nbsp;</td>
599 
          <td>
600 
 
601 
        <center><tt>18h</tt></center>
602 
         </td>
603 
          <td>
604 
 
605 
        <center><tt>3.7</tt></center>
606 
         </td>
607 
         </tr>
608 
 
609 
          <tr>
610 
         <td>
611 
 
612 
        <center><tt>01h</tt></center>
613 
         </td>
614 
          <td>
615 
 
616 
        <center><tt>26.7</tt></center>
617 
         </td>
618 
          <td bgcolor="#cccccc">&nbsp;</td>
619 
          <td>
620 
 
621 
        <center><tt>09h</tt></center>
622 
 
623 
         </td>
624 
          <td>
625 
 
626 
        <center><tt>13.3</tt></center>
627 
         </td>
628 
          <td bgcolor="#cccccc">&nbsp;</td>
629 
          <td>
630 
 
631 
        <center><tt>11h</tt></center>
632 
         </td>
633 
          <td>
634 
 
635 
        <center><tt>6.7</tt></center>
636 
 
637 
         </td>
638 
          <td bgcolor="#cccccc">&nbsp;</td>
639 
          <td>
640 
 
641 
        <center><tt>19h</tt></center>
642 
         </td>
643 
          <td>
644 
 
645 
        <center><tt>3.3</tt></center>
646 
         </td>
647 
         </tr>
648 
 
649 
          <tr>
650 
         <td>
651 
 
652 
        <center><tt>02h</tt></center>
653 
         </td>
654 
          <td>
655 
 
656 
        <center><tt>24.0</tt></center>
657 
         </td>
658 
          <td bgcolor="#cccccc">&nbsp;</td>
659 
          <td>
660 
 
661 
        <center><tt>0Ah</tt></center>
662 
 
663 
         </td>
664 
          <td>
665 
 
666 
        <center><tt>12.0</tt></center>
667 
         </td>
668 
          <td bgcolor="#cccccc">&nbsp;</td>
669 
          <td>
670 
 
671 
        <center><tt>12h</tt></center>
672 
         </td>
673 
          <td>
674 
 
675 
        <center><tt>6.0</tt></center>
676 
 
677 
         </td>
678 
          <td bgcolor="#cccccc">&nbsp;</td>
679 
          <td>
680 
 
681 
        <center><tt>1Ah</tt></center>
682 
         </td>
683 
          <td>
684 
 
685 
        <center><tt>3.0</tt></center>
686 
         </td>
687 
         </tr>
688 
 
689 
          <tr>
690 
         <td>
691 
 
692 
        <center><tt>03h</tt></center>
693 
         </td>
694 
          <td>
695 
 
696 
        <center><tt>21.8</tt></center>
697 
         </td>
698 
          <td bgcolor="#cccccc">&nbsp;</td>
699 
          <td>
700 
 
701 
        <center><tt>0Bh</tt></center>
702 
 
703 
         </td>
704 
          <td>
705 
 
706 
        <center><tt>10.9</tt></center>
707 
         </td>
708 
          <td bgcolor="#cccccc">&nbsp;</td>
709 
          <td>
710 
 
711 
        <center><tt>13h</tt></center>
712 
         </td>
713 
          <td>
714 
 
715 
        <center><tt>5.5</tt></center>
716 
 
717 
         </td>
718 
          <td bgcolor="#cccccc">&nbsp;</td>
719 
          <td>
720 
 
721 
        <center><tt>1Bh</tt></center>
722 
         </td>
723 
          <td>
724 
 
725 
        <center><tt>2.7</tt></center>
726 
         </td>
727 
         </tr>
728 
 
729 
          <tr>
730 
         <td>
731 
 
732 
        <center><tt>04h</tt></center>
733 
         </td>
734 
          <td>
735 
 
736 
        <center><tt>20.7</tt></center>
737 
         </td>
738 
          <td bgcolor="#cccccc">&nbsp;</td>
739 
          <td>
740 
 
741 
        <center><tt>0Ch</tt></center>
742 
 
743 
         </td>
744 
          <td>
745 
 
746 
        <center><tt>10.0</tt></center>
747 
         </td>
748 
          <td bgcolor="#cccccc">&nbsp;</td>
749 
          <td>
750 
 
751 
        <center><tt>14h</tt></center>
752 
         </td>
753 
          <td>
754 
 
755 
        <center><tt>5.0</tt></center>
756 
 
757 
         </td>
758 
          <td bgcolor="#cccccc">&nbsp;</td>
759 
          <td>
760 
 
761 
        <center><tt>1Ch</tt></center>
762 
         </td>
763 
          <td align="center">
764 
                      <font face="Courier New, Courier, monospace"><small>2.5</small></font><br>
765 
                  </td>
766 
         </tr>
767 
 
768 
          <tr>
769 
         <td>
770 
 
771 
        <center><tt>05h</tt></center>
772 
         </td>
773 
          <td>
774 
 
775 
        <center><tt>18.5</tt></center>
776 
         </td>
777 
          <td bgcolor="#cccccc">&nbsp;</td>
778 
          <td>
779 
 
780 
        <center><tt>0Dh</tt></center>
781 
 
782 
         </td>
783 
          <td>
784 
 
785 
        <center><tt>9.2</tt></center>
786 
         </td>
787 
          <td bgcolor="#cccccc">&nbsp;</td>
788 
          <td>
789 
 
790 
        <center><tt>15h</tt></center>
791 
         </td>
792 
          <td>
793 
 
794 
        <center><tt>4.6</tt></center>
795 
 
796 
         </td>
797 
          <td bgcolor="#cccccc">&nbsp;</td>
798 
          <td>
799 
 
800 
        <center><tt>1Dh</tt></center>
801 
         </td>
802 
          <td>
803 
 
804 
        <center><tt>2.3</tt></center>
805 
         </td>
806 
         </tr>
807 
 
808 
          <tr>
809 
         <td>
810 
 
811 
        <center><tt>06h</tt></center>
812 
         </td>
813 
          <td>
814 
 
815 
        <center><tt>17.1</tt></center>
816 
         </td>
817 
          <td bgcolor="#cccccc">&nbsp;</td>
818 
          <td>
819 
 
820 
        <center><tt>0Eh</tt></center>
821 
 
822 
         </td>
823 
          <td>
824 
 
825 
        <center><tt>8.6</tt></center>
826 
         </td>
827 
          <td bgcolor="#cccccc">&nbsp;</td>
828 
          <td>
829 
 
830 
        <center><tt>16h</tt></center>
831 
         </td>
832 
          <td>
833 
 
834 
        <center><tt>4.3</tt></center>
835 
 
836 
         </td>
837 
          <td bgcolor="#cccccc">&nbsp;</td>
838 
          <td>
839 
 
840 
        <center><tt>1Eh</tt></center>
841 
         </td>
842 
          <td>
843 
 
844 
        <center><tt>2.1</tt></center>
845 
         </td>
846 
         </tr>
847 
 
848 
          <tr>
849 
         <td>
850 
 
851 
        <center><tt>07h</tt></center>
852 
         </td>
853 
          <td>
854 
 
855 
        <center><tt>16.0</tt></center>
856 
         </td>
857 
          <td bgcolor="#cccccc">&nbsp;</td>
858 
          <td>
859 
 
860 
        <center><tt>0Fh</tt></center>
861 
 
862 
         </td>
863 
          <td>
864 
 
865 
        <center><tt>8.0</tt></center>
866 
         </td>
867 
          <td bgcolor="#cccccc">&nbsp;</td>
868 
          <td>
869 
 
870 
        <center><tt>17h</tt></center>
871 
         </td>
872 
          <td>
873 
 
874 
        <center><tt>4.0</tt></center>
875 
 
876 
         </td>
877 
          <td bgcolor="#cccccc">&nbsp;</td>
878 
          <td>
879 
 
880 
        <center><tt>1Fh</tt></center>
881 
         </td>
882 
          <td align="center">
883 
                 <small><font face="Courier New, Courier, monospace">2.0</font></small><br>
884 
                  </td>
885 
         </tr>
886 
 
887 
 
888 
 
889 
    </tbody>
890 
  </table>
891 
 
892 
  <div align="center">            </div>
893 
            </center>
894 
 
895 
  <center>
896 
  <p><b>Delay</b></p>
897 
                </center>
898 
 
899 
  <center>
900 
  <table width="217" border="1" cellpadding="0" cellspacing="0" cols="2">
901 
 
902 
         <tbody>
903 
                    <tr>
904 
         <td>
905 
 
906 
        <center>Bits 5-6</center>
907 
         </td>
908 
          <td>
909 
 
910 
        <center>Delay (seconds)</center>
911 
         </td>
912 
         </tr>
913 
 
914 
          <tr>
915 
         <td>
916 
 
917 
        <center>00b</center>
918 
         </td>
919 
          <td>
920 
 
921 
        <center>0.25</center>
922 
         </td>
923 
         </tr>
924 
          <tr>
925 
 
926 
         <td>
927 
 
928 
        <center>01b</center>
929 
         </td>
930 
          <td>
931 
 
932 
        <center>0.50</center>
933 
         </td>
934 
         </tr>
935 
          <tr>
936 
         <td>
937 
 
938 
        <center>10b</center>
939 
 
940 
         </td>
941 
          <td>
942 
 
943 
        <center>0.75</center>
944 
         </td>
945 
         </tr>
946 
          <tr>
947 
         <td>
948 
 
949 
        <center>11b</center>
950 
         </td>
951 
 
952 
          <td>
953 
 
954 
        <center>1.00</center>
955 
         </td>
956 
         </tr>
957 
 
958 
 
959 
    </tbody>
960 
  </table>
961 
                </center>
962 
     <br>
963 
        &nbsp; <li> *0xF2 (Read ID) - The keyboard responds by sending a
964 
two-byte     device ID of 0xAB, 0x83. (0xAB is sent first, followed by 0x83.)</li>
965 
 
966 
     <li> *0xF0 (Set Scan Code Set) -&nbsp; Keyboard responds with "ack",
967 
 then reads argument byte from the host. &nbsp;This argument byte may be 0x01,
968 
  0x02, or 0x03 to select scan code set 1, 2, or 3, respectively.&nbsp; The
969 
  keyboard responds to this argument byte with "ack". &nbsp;If the argument
970 
  byte is 0x00, the keyboard responds with "ack" followed by the current scan
971 
  code set.</li>
972 
     <li> 0xEE (Echo) - The keyboard responds with "Echo" (0xEE).</li>
973 
     <li> 0xED (Set/Reset LEDs) - The host follows this command with one
974 
 argument    byte, that specifies the state of the keyboard's Num Lock, Caps
975 
 Lock, and   Scroll Lock LEDs.&nbsp; This argument byte is defined as follows:</li>
976 
 
977 
 
978 
</ul>
979 
 
980 
<center>
981 
<table width="400" border="0" cellpadding="3" cellspacing="0" cols="8">
982 
         <tbody>
983 
                  <tr valign="CENTER" align="center">
984 
         <td>MSb</td>
985 
          <td><br>
986 
                    </td>
987 
          <td><br>
988 
 
989 
                    </td>
990 
          <td><br>
991 
                    </td>
992 
          <td><br>
993 
                    </td>
994 
          <td><br>
995 
                    </td>
996 
          <td><br>
997 
                    </td>
998 
 
999 
          <td>LSb</td>
1000 
         </tr>
1001 
 
1002 
  </tbody>
1003 
</table>
1004 
              </center>
1005 
 
1006 
<center>
1007 
<table width="400" border="1" cellpadding="2" cellspacing="0" cols="8">
1008 
         <tbody>
1009 
                  <tr valign="CENTER" align="center">
1010 
 
1011 
         <td>Always 0</td>
1012 
          <td>Always 0</td>
1013 
          <td>Always 0</td>
1014 
          <td>Always 0</td>
1015 
          <td>Always 0</td>
1016 
          <td>Caps Lock</td>
1017 
 
1018 
          <td>Num Lock</td>
1019 
          <td>Scroll Lock</td>
1020 
         </tr>
1021 
 
1022 
  </tbody>
1023 
</table>
1024 
              </center>
1025 
 
1026 
<blockquote>
1027 
  <blockquote>
1028 
 
1029 
    <blockquote>
1030 
 
1031 
      <ul>
1032 
 
1033 
 
1034 
        <ul>
1035 
             <li> "Scroll Lock" - Scroll Lock LED off(0)/on(1)</li>
1036 
             <li> "Num Lock" - Num Lock LED off(0)/on(1)</li>
1037 
             <li> "Caps Lock" - Caps Lock LED off(0)/on(1)</li>
1038 
 
1039 
        </ul>
1040 
 
1041 
      </ul>
1042 
 
1043 
         </blockquote>
1044 
         </blockquote>
1045 
         </blockquote>
1046 
         *Originally available in PS/2 keyboards only.
1047 
 
1048 
<p><b>Emulation:</b> </p>
1049 
 
1050 
<ul>
1051 
        Click here   for keyboard/mouse routines.&nbsp; Source in MPASM for
1052 
 PIC microcontrollers.
1053 
 
1054 
</ul>
1055 
         <b>The i8042 Keyboard Controller:</b>
1056 
 
1057 
<p>Up to this point in the article, all information has been presented
1058 
from a hardware point-of-view.&nbsp; However, if you're writing low-level
1059 
    keyboard-related software for the host PC, you won't be communicating
1060 
directly    with the keyboard.&nbsp; Instead, a keyboard controller provides
1061 
an interface    between the keyboard and the peripheral bus.&nbsp; This controller
1062 
takes   care of all the signal-level and protocol details, as well as providing
1063 
 some  conversion, interpretation, and handling of scan codes and commands.&nbsp;
1064 
         </p>
1065 
 
1066 
<p>An Intel 8042/compatible microcontroller is used as the PC's keyboard
1067 
  controller.&nbsp; In modern computers, this microcontroller is hidden within
1068 
   the motherboard's chipset, which integrates many controllers in a single
1069 
  package.&nbsp; Nonetheless, this device is still there, and the keyboard
1070 
 controller is still commonly referred to as "the 8042". </p>
1071 
 
1072 
 
1073 
<p>Depending on the motherboard, the keyboard controller may operate   in
1074 
 one of two modes: "AT-compatible" mode, or "PS/2-compatible" mode.&nbsp;
1075 
   The latter is used if a PS/2 mouse is supported by the motherboard.&nbsp;
1076 
    If this is the case, the 8042 acts as the keyboard controller and the
1077 
mouse    controller.&nbsp; The keyboard controller auto-detects which mode
1078 
it is  to use according to how it's wired to the keyboard port. </p>
1079 
 
1080 
<p>The 8042 contains the following registers: </p>
1081 
 
1082 
<ul>
1083 
     <li> A one-byte input buffer - contains byte read from keyboard; read-only</li>
1084 
 
1085 
     <li> A one-byte output buffer - contains byte to-be-written to keyboard;
1086 
    write-only</li>
1087 
     <li> A one-byte status register - 8 status flags; read-only</li>
1088 
     <li> A one-byte control register - 7 control flags; read/write&nbsp;</li>
1089 
 
1090 
</ul>
1091 
         The first three registers (input, output, status) are directly accessible
1092 
    via ports 0x60 and 0x64.&nbsp; The last register (control) is read using
1093 
   the "Read Command Byte" command, and written using the "Write Command Byte"
1094 
   command.&nbsp; The following table shows how the peripheral ports are
1095 
used    to interface the 8042: <br>
1096 
 
1097 
        &nbsp;
1098 
<center>
1099 
<table border="1" cellpadding="3" cellspacing="0">
1100 
         <tbody>
1101 
                  <tr>
1102 
         <td>
1103 
 
1104 
      <center>Port</center>
1105 
         </td>
1106 
          <td>
1107 
 
1108 
      <center>Read /&nbsp; <br>
1109 
 
1110 
        Write</center>
1111 
         </td>
1112 
          <td>
1113 
 
1114 
      <center>Function</center>
1115 
         </td>
1116 
         </tr>
1117 
          <tr>
1118 
         <td>0x60</td>
1119 
 
1120 
          <td>Read</td>
1121 
          <td>Read Input Buffer</td>
1122 
         </tr>
1123 
          <tr>
1124 
         <td>0x60</td>
1125 
          <td>Write</td>
1126 
          <td>Write Output Buffer</td>
1127 
 
1128 
         </tr>
1129 
          <tr>
1130 
         <td>0x64</td>
1131 
          <td>Read</td>
1132 
          <td>Read Status Register</td>
1133 
         </tr>
1134 
          <tr>
1135 
 
1136 
         <td>0x64</td>
1137 
          <td>Write</td>
1138 
          <td>Send Command</td>
1139 
         </tr>
1140 
 
1141 
  </tbody>
1142 
</table>
1143 
              </center>
1144 
 
1145 
 
1146 
<p>Writing to port 0x64 doesn't write to any specific register, but   sends
1147 
 a command for the 8042 to interpret.&nbsp; If the command accepts a  parameter,
1148 
 this parameter is sent to port 0x60.&nbsp; Likewise, any results   returned
1149 
 by the command may be read from port 0x60. </p>
1150 
 
1151 
<p>When describing the 8042, I may occasionally refer to its physical   I/O
1152 
 pins.&nbsp; These pins are defined below: </p>
1153 
 
1154 
<p><u>AT-compatible mode</u> </p>
1155 
 
1156 
<center>
1157 
 
1158 
<table border="0" cellpadding="5" cellspacing="0">
1159 
         <tbody>
1160 
                  <tr>
1161 
         <td>Port 1 (Input Port):
1162 
 
1163 
      <center>
1164 
 
1165 
      <table border="1" cellpadding="2" cellspacing="0">
1166 
         <tbody>
1167 
                        <tr>
1168 
         <td>Pin</td>
1169 
          <td>Name</td>
1170 
 
1171 
          <td>Function</td>
1172 
         </tr>
1173 
          <tr>
1174 
         <td>0</td>
1175 
          <td>P10</td>
1176 
          <td> <br>
1177 
        Undefined <br>
1178 
 
1179 
        .</td>
1180 
         </tr>
1181 
          <tr>
1182 
         <td>1</td>
1183 
          <td>P11</td>
1184 
          <td> <br>
1185 
        Undefined <br>
1186 
 
1187 
        .</td>
1188 
         </tr>
1189 
          <tr>
1190 
         <td>2</td>
1191 
          <td>P12</td>
1192 
          <td> <br>
1193 
        Undefined <br>
1194 
 
1195 
        .</td>
1196 
         </tr>
1197 
          <tr>
1198 
         <td>3</td>
1199 
          <td>P13</td>
1200 
          <td> <br>
1201 
        Undefined <br>
1202 
 
1203 
        .</td>
1204 
         </tr>
1205 
          <tr>
1206 
         <td>4</td>
1207 
          <td>P14</td>
1208 
          <td>External RAM <br>
1209 
        1: Enable external RAM <br>
1210 
 
1211 
        0: Disable external RAM</td>
1212 
         </tr>
1213 
          <tr>
1214 
         <td>5</td>
1215 
          <td>P15</td>
1216 
          <td>Manufacturing Setting <br>
1217 
        1: Setting enabled <br>
1218 
 
1219 
        0: Setting disabled</td>
1220 
         </tr>
1221 
          <tr>
1222 
         <td>6</td>
1223 
          <td>P16</td>
1224 
          <td>Display Type Switch <br>
1225 
        1: Color display <br>
1226 
 
1227 
        0: Monochrome</td>
1228 
         </tr>
1229 
          <tr>
1230 
         <td>7</td>
1231 
          <td>P17</td>
1232 
          <td>Keyboard Inhibit Switch <br>
1233 
        1: Keyboard enabled <br>
1234 
 
1235 
        0: Keyboard inhibited</td>
1236 
         </tr>
1237 
 
1238 
 
1239 
        </tbody>
1240 
 
1241 
      </table>
1242 
                    </center>
1243 
         </td>
1244 
          <td>Port 2 (Output Port):
1245 
 
1246 
      <table border="1" cellpadding="2" cellspacing="0">
1247 
         <tbody>
1248 
 
1249 
                        <tr>
1250 
         <td>Pin</td>
1251 
          <td>Name</td>
1252 
          <td>Function</td>
1253 
         </tr>
1254 
          <tr>
1255 
         <td>0</td>
1256 
 
1257 
          <td>P20</td>
1258 
          <td>System Reset <br>
1259 
        1: Normal <br>
1260 
        0: Reset computer</td>
1261 
         </tr>
1262 
          <tr>
1263 
         <td>1</td>
1264 
 
1265 
          <td>P21</td>
1266 
          <td> <br>
1267 
        Gate A20 <br>
1268 
        .</td>
1269 
         </tr>
1270 
          <tr>
1271 
         <td>2</td>
1272 
 
1273 
          <td>P22</td>
1274 
          <td> <br>
1275 
        Undefined <br>
1276 
        .</td>
1277 
         </tr>
1278 
          <tr>
1279 
         <td>3</td>
1280 
 
1281 
          <td>P23</td>
1282 
          <td> <br>
1283 
        Undefined <br>
1284 
        .</td>
1285 
         </tr>
1286 
          <tr>
1287 
         <td>4</td>
1288 
 
1289 
          <td>P24</td>
1290 
          <td> <br>
1291 
        Input Buffer Full <br>
1292 
        .</td>
1293 
         </tr>
1294 
          <tr>
1295 
         <td>5</td>
1296 
 
1297 
          <td>P25</td>
1298 
          <td> <br>
1299 
        Output Buffer Empty <br>
1300 
        .</td>
1301 
         </tr>
1302 
          <tr>
1303 
         <td>6</td>
1304 
 
1305 
          <td>P26</td>
1306 
          <td>Keyboard Clock <br>
1307 
        1: Pull Clock low <br>
1308 
        0: High-Z</td>
1309 
         </tr>
1310 
          <tr>
1311 
         <td>7</td>
1312 
 
1313 
          <td>P27</td>
1314 
          <td>Keyboard Data: <br>
1315 
        1: Pull Data low <br>
1316 
        0: High-Z</td>
1317 
         </tr>
1318 
 
1319 
 
1320 
        </tbody>
1321 
 
1322 
      </table>
1323 
 
1324 
         </td>
1325 
          <td>Port 3 (Test Port):
1326 
 
1327 
      <center>
1328 
 
1329 
      <table border="1" cellpadding="2" cellspacing="0">
1330 
         <tbody>
1331 
                        <tr>
1332 
         <td>Pin</td>
1333 
          <td>Name</td>
1334 
          <td>Function</td>
1335 
 
1336 
         </tr>
1337 
          <tr>
1338 
         <td>0</td>
1339 
          <td>T0</td>
1340 
          <td>Keyboard Clock&nbsp; <br>
1341 
        (Input) <br>
1342 
 
1343 
        .</td>
1344 
         </tr>
1345 
          <tr>
1346 
         <td>1</td>
1347 
          <td>T1</td>
1348 
          <td>Keyboard Data <br>
1349 
        (Input) <br>
1350 
 
1351 
        .</td>
1352 
         </tr>
1353 
          <tr>
1354 
         <td>2</td>
1355 
          <td>--</td>
1356 
          <td> <br>
1357 
        Undefined <br>
1358 
 
1359 
        .</td>
1360 
         </tr>
1361 
          <tr>
1362 
         <td>3</td>
1363 
          <td>--</td>
1364 
          <td> <br>
1365 
        Undefined <br>
1366 
 
1367 
        .</td>
1368 
         </tr>
1369 
          <tr>
1370 
         <td>4</td>
1371 
          <td>--</td>
1372 
          <td> <br>
1373 
        Undefined <br>
1374 
 
1375 
        .</td>
1376 
         </tr>
1377 
          <tr>
1378 
         <td>5</td>
1379 
          <td>--</td>
1380 
          <td> <br>
1381 
        Undefined <br>
1382 
 
1383 
        .</td>
1384 
         </tr>
1385 
          <tr>
1386 
         <td>6</td>
1387 
          <td>--</td>
1388 
          <td> <br>
1389 
        Undefined <br>
1390 
 
1391 
        .</td>
1392 
         </tr>
1393 
          <tr>
1394 
         <td>7</td>
1395 
          <td>--</td>
1396 
          <td> <br>
1397 
        Undefined <br>
1398 
 
1399 
        .</td>
1400 
         </tr>
1401 
 
1402 
 
1403 
        </tbody>
1404 
 
1405 
      </table>
1406 
                    </center>
1407 
         </td>
1408 
         </tr>
1409 
 
1410 
  </tbody>
1411 
</table>
1412 
 
1413 
              </center>
1414 
 
1415 
<p><u>PS/2-compatible mode</u> </p>
1416 
 
1417 
<center>
1418 
<table border="0" cellpadding="5" cellspacing="0">
1419 
         <tbody>
1420 
                  <tr>
1421 
         <td>Port 1 (Input Port):
1422 
 
1423 
      <center>
1424 
 
1425 
      <table border="1" cellpadding="2" cellspacing="0">
1426 
 
1427 
         <tbody>
1428 
                        <tr>
1429 
         <td>Pin</td>
1430 
          <td>Name</td>
1431 
          <td>Function</td>
1432 
         </tr>
1433 
          <tr>
1434 
 
1435 
         <td>0</td>
1436 
          <td>P10</td>
1437 
          <td>Keyboard Data <br>
1438 
        (Input) <br>
1439 
        .</td>
1440 
         </tr>
1441 
 
1442 
          <tr>
1443 
         <td>1</td>
1444 
          <td>P11</td>
1445 
          <td>Mouse Data <br>
1446 
        (Input) <br>
1447 
        .</td>
1448 
 
1449 
         </tr>
1450 
          <tr>
1451 
         <td>2</td>
1452 
          <td>P12</td>
1453 
          <td> <br>
1454 
        Undefined <br>
1455 
        .</td>
1456 
 
1457 
         </tr>
1458 
          <tr>
1459 
         <td>3</td>
1460 
          <td>P13</td>
1461 
          <td> <br>
1462 
        Undefined <br>
1463 
        .</td>
1464 
 
1465 
         </tr>
1466 
          <tr>
1467 
         <td>4</td>
1468 
          <td>P14</td>
1469 
          <td>External RAM <br>
1470 
        1: Enable external RAM <br>
1471 
        0: Disable external RAM</td>
1472 
 
1473 
         </tr>
1474 
          <tr>
1475 
         <td>5</td>
1476 
          <td>P15</td>
1477 
          <td>Manufacturing Setting <br>
1478 
        1: Setting enabled <br>
1479 
        0: Setting disabled</td>
1480 
 
1481 
         </tr>
1482 
          <tr>
1483 
         <td>6</td>
1484 
          <td>P16</td>
1485 
          <td>Display Type Switch <br>
1486 
        1: Color display <br>
1487 
        0: Monochrome</td>
1488 
 
1489 
         </tr>
1490 
          <tr>
1491 
         <td>7</td>
1492 
          <td>P17</td>
1493 
          <td>Keyboard Inhibit Switch <br>
1494 
        1: Keyboard enabled <br>
1495 
        0: Keyboard disabled</td>
1496 
 
1497 
         </tr>
1498 
 
1499 
 
1500 
        </tbody>
1501 
 
1502 
      </table>
1503 
                    </center>
1504 
         </td>
1505 
          <td>Port 2 (Output Port):
1506 
 
1507 
      <center>
1508 
 
1509 
      <table border="1" cellpadding="2" cellspacing="0">
1510 
         <tbody>
1511 
                        <tr>
1512 
 
1513 
         <td>Pin</td>
1514 
          <td>Name</td>
1515 
          <td>Function</td>
1516 
         </tr>
1517 
          <tr>
1518 
         <td>0</td>
1519 
          <td>P20</td>
1520 
 
1521 
          <td>System Reset <br>
1522 
        1: Normal <br>
1523 
        0: Reset computer</td>
1524 
         </tr>
1525 
          <tr>
1526 
         <td>1</td>
1527 
          <td>P21</td>
1528 
 
1529 
          <td> <br>
1530 
        Gate A20 <br>
1531 
        .</td>
1532 
         </tr>
1533 
          <tr>
1534 
         <td>2</td>
1535 
          <td>P22</td>
1536 
 
1537 
          <td>Mouse Data: <br>
1538 
        1: Pull Data low <br>
1539 
        0: High-Z</td>
1540 
         </tr>
1541 
          <tr>
1542 
         <td>3</td>
1543 
          <td>P23</td>
1544 
 
1545 
          <td>Mouse Clock: <br>
1546 
        1: Pull Clock low <br>
1547 
        0: High-Z</td>
1548 
         </tr>
1549 
          <tr>
1550 
         <td>4</td>
1551 
          <td>P24</td>
1552 
 
1553 
          <td>Keyboard IBF interrupt: <br>
1554 
        1: Assert IRQ 1 <br>
1555 
        0: De-assert IRQ 1</td>
1556 
         </tr>
1557 
          <tr>
1558 
         <td>5</td>
1559 
          <td>P25</td>
1560 
 
1561 
          <td>Mouse IBF interrupt: <br>
1562 
        1: Assert IRQ 12 <br>
1563 
        0: De-assert IRQ 12</td>
1564 
         </tr>
1565 
          <tr>
1566 
         <td>6</td>
1567 
          <td>P26</td>
1568 
 
1569 
          <td>Keyboard Clock: <br>
1570 
        1: Pull Clock low <br>
1571 
        0: High-Z</td>
1572 
         </tr>
1573 
          <tr>
1574 
         <td>7</td>
1575 
          <td>P27</td>
1576 
 
1577 
          <td>Keyboard Data: <br>
1578 
        1: Pull Data low <br>
1579 
        0: High-Z</td>
1580 
         </tr>
1581 
 
1582 
 
1583 
        </tbody>
1584 
 
1585 
      </table>
1586 
                    </center>
1587 
         </td>
1588 
 
1589 
          <td>Port 3 (Test Port):
1590 
 
1591 
      <center>
1592 
 
1593 
      <table border="1" cellpadding="2" cellspacing="0">
1594 
         <tbody>
1595 
                        <tr>
1596 
         <td>Pin</td>
1597 
          <td>Name</td>
1598 
          <td>Function</td>
1599 
 
1600 
         </tr>
1601 
          <tr>
1602 
         <td>0</td>
1603 
          <td>T0</td>
1604 
          <td>Keyboard Clock <br>
1605 
        (Input) <br>
1606 
        .</td>
1607 
 
1608 
         </tr>
1609 
          <tr>
1610 
         <td>1</td>
1611 
          <td>T1</td>
1612 
          <td>Mouse Clock <br>
1613 
        (Input) <br>
1614 
        .</td>
1615 
 
1616 
         </tr>
1617 
          <tr>
1618 
         <td>2</td>
1619 
          <td>--</td>
1620 
          <td> <br>
1621 
        Undefined <br>
1622 
        .</td>
1623 
 
1624 
         </tr>
1625 
          <tr>
1626 
         <td>3</td>
1627 
          <td>--</td>
1628 
          <td> <br>
1629 
        Undefined <br>
1630 
        .</td>
1631 
 
1632 
         </tr>
1633 
          <tr>
1634 
         <td>4</td>
1635 
          <td>--</td>
1636 
          <td> <br>
1637 
        Undefined <br>
1638 
        .</td>
1639 
 
1640 
         </tr>
1641 
          <tr>
1642 
         <td>5</td>
1643 
          <td>--</td>
1644 
          <td> <br>
1645 
        Undefined <br>
1646 
        .</td>
1647 
 
1648 
         </tr>
1649 
          <tr>
1650 
         <td>6</td>
1651 
          <td>--</td>
1652 
          <td> <br>
1653 
        Undefined <br>
1654 
        .</td>
1655 
 
1656 
         </tr>
1657 
          <tr>
1658 
         <td>7</td>
1659 
          <td>--</td>
1660 
          <td> <br>
1661 
        Undefined <br>
1662 
        .</td>
1663 
 
1664 
         </tr>
1665 
 
1666 
 
1667 
        </tbody>
1668 
 
1669 
      </table>
1670 
                    </center>
1671 
         </td>
1672 
         </tr>
1673 
 
1674 
  </tbody>
1675 
</table>
1676 
              </center>
1677 
 
1678 
 
1679 
<p>(Note: Reading keyboard controller datasheets can be confusing--it   will
1680 
 refer to the "input buffer" as the "output buffer" and vice versa.&nbsp;
1681 
   This makes sense from the point-of-view of someone writing firmware for
1682 
  the controller, but for somebody used to interfacing the controller, this
1683 
  can cause problems.&nbsp; Throughout this document, I only refer to the
1684 
"input   buffer" as the one containing input from the keyboard, and the "output
1685 
  buffer"   as the one that contains output to be sent to the keyboard.)
1686 
</p>
1687 
 
1688 
<p><i>Status Register:</i> </p>
1689 
 
1690 
<p>The 8042's status flags are read from port 0x64.&nbsp; They contain
1691 
error information, status information, and indicate whether or not data
1692 
is present in the input and output buffers.&nbsp; The flags are defined as
1693 
 follows:        <br>
1694 
 
1695 
        &nbsp; </p>
1696 
 
1697 
<center>
1698 
<table border="0" cellpadding="0" cellspacing="0">
1699 
         <tbody>
1700 
                  <tr>
1701 
         <td><br>
1702 
                    </td>
1703 
          <td>
1704 
 
1705 
      <center>
1706 
 
1707 
      <table width="400" border="0" cellpadding="3" cellspacing="0" cols="8">
1708 
 
1709 
         <tbody>
1710 
                        <tr>
1711 
         <td>MSb</td>
1712 
          <td><br>
1713 
                          </td>
1714 
          <td><br>
1715 
                          </td>
1716 
          <td><br>
1717 
 
1718 
                          </td>
1719 
          <td><br>
1720 
                          </td>
1721 
          <td><br>
1722 
                          </td>
1723 
          <td><br>
1724 
                          </td>
1725 
          <td>
1726 
 
1727 
 
1728 
            <div align="right">LSb</div>
1729 
 
1730 
         </td>
1731 
         </tr>
1732 
 
1733 
 
1734 
        </tbody>
1735 
 
1736 
      </table>
1737 
                    </center>
1738 
         </td>
1739 
         </tr>
1740 
          <tr>
1741 
         <td>AT-compatible mode:</td>
1742 
 
1743 
          <td>
1744 
 
1745 
      <center>
1746 
 
1747 
      <table width="400" border="1" cellpadding="2" cellspacing="0" cols="8">
1748 
         <tbody>
1749 
                        <tr>
1750 
         <td>
1751 
 
1752 
 
1753 
            <center>PERR</center>
1754 
         </td>
1755 
          <td>
1756 
 
1757 
 
1758 
            <center>RxTO</center>
1759 
 
1760 
         </td>
1761 
          <td>
1762 
 
1763 
 
1764 
            <center>TxTO</center>
1765 
         </td>
1766 
          <td>
1767 
 
1768 
 
1769 
            <center>INH</center>
1770 
         </td>
1771 
          <td>
1772 
 
1773 
 
1774 
            <center>A2</center>
1775 
 
1776 
         </td>
1777 
          <td>
1778 
 
1779 
 
1780 
            <center>SYS</center>
1781 
         </td>
1782 
          <td>
1783 
 
1784 
 
1785 
            <center>IBF</center>
1786 
         </td>
1787 
          <td>
1788 
 
1789 
 
1790 
            <center>OBF</center>
1791 
 
1792 
         </td>
1793 
         </tr>
1794 
 
1795 
 
1796 
        </tbody>
1797 
 
1798 
      </table>
1799 
                    </center>
1800 
         </td>
1801 
         </tr>
1802 
          <tr>
1803 
         <td>PS/2-compatible mode:&nbsp;</td>
1804 
 
1805 
          <td>
1806 
 
1807 
      <center>
1808 
 
1809 
      <table width="400" border="1" cellpadding="2" cellspacing="0" cols="8">
1810 
         <tbody>
1811 
                        <tr>
1812 
         <td>
1813 
 
1814 
 
1815 
            <center>PERR</center>
1816 
         </td>
1817 
          <td>
1818 
 
1819 
 
1820 
            <center>TO</center>
1821 
 
1822 
         </td>
1823 
          <td>
1824 
 
1825 
 
1826 
            <center>MOBF</center>
1827 
         </td>
1828 
          <td>
1829 
 
1830 
 
1831 
            <center>INH</center>
1832 
         </td>
1833 
          <td>
1834 
 
1835 
 
1836 
            <center>A2</center>
1837 
 
1838 
         </td>
1839 
          <td>
1840 
 
1841 
 
1842 
            <center>SYS</center>
1843 
         </td>
1844 
          <td>
1845 
 
1846 
 
1847 
            <center>IBF</center>
1848 
         </td>
1849 
          <td>
1850 
 
1851 
 
1852 
            <center>OBF</center>
1853 
 
1854 
         </td>
1855 
         </tr>
1856 
 
1857 
 
1858 
        </tbody>
1859 
 
1860 
      </table>
1861 
                    </center>
1862 
         </td>
1863 
         </tr>
1864 
 
1865 
  </tbody>
1866 
</table>
1867 
              </center>
1868 
 
1869 
 
1870 
<ul>
1871 
     <li> OBF (Output Buffer Full) - Indicates when it's okay to write to
1872 
 output   buffer.</li>
1873 
     <br>
1874 
        0: Output buffer empty - Okay to write to port 0x60 <br>
1875 
        1: Output buffer full - Don't write to port 0x60 <li> IBF (Input
1876 
Buffer    Full) - Indicates when input is available in the input buffer.</li>
1877 
     <br>
1878 
 
1879 
        0: Input buffer empty - No unread input at port 0x60 <br>
1880 
        1: Input buffer full - New input can be read from port 0x60 <li>
1881 
SYS   (System   flag) - Post reads this to determine if power-on reset, or
1882 
software   reset.</li>
1883 
     <br>
1884 
        0: Power-up value - System is in power-on reset. <br>
1885 
        1: BAT code received - System has already beed initialized. <li>
1886 
A2  (Address   line A2) - Used internally by the keyboard controller</li>
1887 
 
1888 
     <br>
1889 
        0: A2 = 0 - Port 0x60 was last written to <br>
1890 
        1: A2 = 1 - Port 0x64 was last written to <li> INH (Inhibit flag)
1891 
-  Indicates   whether or not keyboard communication is inhibited.</li>
1892 
     <br>
1893 
        0: Keyboard Clock = 0 - Keyboard is inhibited <br>
1894 
        1: Keyboard Clock = 1 - Keyboard is not inhibited <li> TxTO (Transmit
1895 
  Timeout)  - Indicates keyboard isn't accepting input (kbd may not be plugged
1896 
  in).</li>
1897 
 
1898 
     <br>
1899 
        0: No Error - Keyboard accepted the last byte written to it. <br>
1900 
        1: Timeout error - Keyboard didn't generate clock signals within
1901 
15  ms  of  "request-to-send". <li> RxTO (Receive Timeout) - Indicates keyboard
1902 
  didn't   respond to a command (kbd probably broke)</li>
1903 
     <br>
1904 
        0: No Error - Keyboard responded to last byte. <br>
1905 
        1: Timeout error - Keyboard didn't generate clock signals within
1906 
20  ms  of  command reception. <li> PERR (Parity Error) - Indicates communication
1907 
   error  with keyboard (possibly noisy/loose connection)</li>
1908 
 
1909 
     <br>
1910 
        0: No Error - Odd parity received and proper command response recieved.
1911 
           <br>
1912 
        1: Parity Error - Even parity received or 0xFE received as command
1913 
 response.            <li> MOBF (Mouse Output Buffer Full) - Similar to OBF,
1914 
 except for   PS/2 mouse.</li>
1915 
     <br>
1916 
        0: Output buffer empty - Okay to write to auxillary device's output
1917 
 buffer            <br>
1918 
        1: Output buffer full - Don't write to port auxillary device's output
1919 
  buffer           <li> TO (General Timout) - Indicates timeout during command
1920 
  write  or response. (Same as TxTO + RxTO.)</li>
1921 
 
1922 
     <br>
1923 
        0: No Error - Keyboard received and responded to last command. <br>
1924 
        1: Timeout Error - See TxTO and RxTO for more information.
1925 
 
1926 
</ul>
1927 
         [EG: On my PC, the normal value of the 8042's "Status" register
1928 
is  14h   = 00010100b.&nbsp; This indicates keyboard communication is not
1929 
inhibited,    and the 8042 has already completed its self-test ("BAT").&nbsp;
1930 
The "Status"    register is accessed by reading from port 64h ("IN AL, 64h")]
1931 
 
1932 
<p><i>Reading keyboard input:</i> </p>
1933 
 
1934 
 
1935 
<p>When the 8042 recieves a valid scan code from the keyboard, it is   converted
1936 
 to its set 1 equivalent.&nbsp; The converted scan code is then  placed in
1937 
 the input buffer, the IBF (Input Buffer Full) flag is set, and IRQ 1 is asserted.&nbsp;
1938 
 Furthermore, when any byte is received from the keyboard, the 8042 inhibits
1939 
 further reception (by pulling the "Clock" line low), so no other scan codes
1940 
 will be received until the input buffer is emptied.        </p>
1941 
 
1942 
<p>If enabled, IRQ 1 will activate the keyboard driver, pointed to by interrupt
1943 
 vector 0x09.&nbsp; The driver reads the scan code from port 0x60, which causes
1944 
 the 8042 to de-assert IRQ 1 and reset the IBF flag.&nbsp; The scan code
1945 
is  then processed by the driver, which responds to special key combinations
1946 
and updates an area of the system RAM reserved for keyboard input.       </p>
1947 
 
1948 
<p>If you don't want to patch into interrupt 0x09, you may poll the   keyboard
1949 
 controller for input.&nbsp; This is accomplished by disabling the   8042's
1950 
 IBF Interrupt and polling the IBF flag.&nbsp; This flag is set (1)   when
1951 
 data is available in the input buffer, and is cleared (0) when data  is read
1952 
 from the input buffer.&nbsp; Reading the input buffer is accomplished
1953 
 by reading from port 0x60, and the IBF flag is at port 0x64, bit 1.&nbsp;
1954 
   The following assembly code illustrates this: </p>
1955 
 
1956 
 
1957 
<p><tt>kbRead:</tt> <br>
1958 
              <tt>WaitLoop:&nbsp;&nbsp;&nbsp; in&nbsp;&nbsp;&nbsp;&nbsp;
1959 
al,   64h&nbsp;&nbsp;&nbsp;&nbsp;   ; Read Status byte</tt> <br>
1960 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1961 
    and&nbsp;&nbsp;&nbsp; al, 10b&nbsp;&nbsp;&nbsp;&nbsp; ; Test IBF flag
1962 
(Status&lt;1&gt;)</tt>          <br>
1963 
 
1964 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1965 
    jz&nbsp;&nbsp;&nbsp;&nbsp; WaitLoop&nbsp;&nbsp;&nbsp; ; Wait for IBF =
1966 
 1</tt>         <br>
1967 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1968 
    in&nbsp;&nbsp;&nbsp;&nbsp; al, 60h&nbsp;&nbsp;&nbsp;&nbsp; ; Read input
1969 
  buffer</tt>        </p>
1970 
 
1971 
 
1972 
<p><i>Writing to keyboard:</i> </p>
1973 
 
1974 
<p>When you write to the 8042's output buffer (via port 0x60), the controller
1975 
 sets the OBF ("Output Buffer Full") flag and processes the data.&nbsp;  The
1976 
 8042 will send this data to the keyboard and wait for a response.&nbsp;
1977 
If the keyboard does not accept or generate a response within a given amount
1978 
    of time, the appropriate timeout flag will be set (see Status register
1979 
 definition  for more info.)&nbsp; If an incorrect parity bit is read, the
1980 
 8042 will send  the "Resend" (0xFE) command to the keyboard.&nbsp; If the
1981 
 keyboard continues  to send erroneous bytes, the "Parity Error" flag is set
1982 
 in the Status register.&nbsp;  If no errors occur, the response byte is
1983 
placed  in the input buffer, the IBF ("Input Buffer Full") flag is set, and
1984 
IRQ 1  is activated, signaling the keyboard driver. </p>
1985 
 
1986 
 
1987 
<p>The following assembly code shows how to write to the output buffer.&nbsp;
1988 
    (Remember, after you write to the output buffer, you should use int 9h
1989 
 or  poll port 64h to get the keyboard's response.) </p>
1990 
 
1991 
<p><tt>kbWrite:</tt> <br>
1992 
              <tt>WaitLoop:&nbsp;&nbsp;&nbsp; in&nbsp;&nbsp;&nbsp;&nbsp;
1993 
al,   64h&nbsp;&nbsp;&nbsp;&nbsp;   ; Read Status byte</tt> <br>
1994 
 
1995 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1996 
    and&nbsp;&nbsp;&nbsp; al, 01b&nbsp;&nbsp;&nbsp;&nbsp; ; Test OBF flag
1997 
(Status&lt;0&gt;)</tt>          <br>
1998 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
1999 
    jnz&nbsp;&nbsp;&nbsp; WaitLoop&nbsp;&nbsp;&nbsp; ; Wait for OBF = 0</tt>
2000 
         <br>
2001 
 
2002 
              <tt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
2003 
    out&nbsp;&nbsp;&nbsp; 60h, cl&nbsp;&nbsp;&nbsp;&nbsp; ; Write data to
2004 
output    buffer</tt> </p>
2005 
 
2006 
<p><i>Keyboard Controller Commands:</i> </p>
2007 
 
2008 
<p>Commands are sent to the keyboard controller by writing to port 0x64.&nbsp;
2009 
 Command parameters are written to port 0x60 after teh command is sent.&nbsp;
2010 
 Results are returned on port 0x60.&nbsp; Always test the OBF ("Output Buffer
2011 
 Full") flag before writing commands or parameters to the 8042. </p>
2012 
 
2013 
 
2014 
<ul>
2015 
     <li> 0x20 (Read Command Byte) - Returns command byte.&nbsp; (See "Write
2016 
    Command Byte" below).</li>
2017 
     <li> 0x60 (Write Command Byte) - Stores parameter as command byte.&nbsp;
2018 
    Command byte defined as follows:</li>
2019 
 
2020 
</ul>
2021 
 
2022 
 
2023 
<center>
2024 
<table border="0" cellpadding="0" cellspacing="0">
2025 
         <tbody>
2026 
                  <tr>
2027 
         <td><br>
2028 
                    </td>
2029 
          <td>
2030 
 
2031 
      <center>
2032 
 
2033 
      <table width="400" border="0" cellpadding="3" cellspacing="0" cols="8">
2034 
         <tbody>
2035 
 
2036 
                        <tr>
2037 
         <td>MSb</td>
2038 
          <td><br>
2039 
                          </td>
2040 
          <td><br>
2041 
                          </td>
2042 
          <td><br>
2043 
                          </td>
2044 
 
2045 
          <td><br>
2046 
                          </td>
2047 
          <td><br>
2048 
                          </td>
2049 
          <td><br>
2050 
                          </td>
2051 
          <td>
2052 
 
2053 
 
2054 
            <div align="right">LSb</div>
2055 
         </td>
2056 
 
2057 
         </tr>
2058 
 
2059 
 
2060 
        </tbody>
2061 
 
2062 
      </table>
2063 
                    </center>
2064 
         </td>
2065 
         </tr>
2066 
          <tr>
2067 
         <td>AT-compatible mode:</td>
2068 
          <td>
2069 
 
2070 
      <center>
2071 
 
2072 
      <table width="400" border="1" cellpadding="2" cellspacing="0" cols="8">
2073 
 
2074 
         <tbody>
2075 
                        <tr>
2076 
         <td>
2077 
 
2078 
 
2079 
            <center>--</center>
2080 
         </td>
2081 
          <td>
2082 
 
2083 
 
2084 
            <center>XLAT</center>
2085 
         </td>
2086 
          <td>
2087 
 
2088 
 
2089 
            <center>PC</center>
2090 
 
2091 
         </td>
2092 
          <td>
2093 
 
2094 
 
2095 
            <center>_EN</center>
2096 
         </td>
2097 
          <td>
2098 
 
2099 
 
2100 
            <center>OVR</center>
2101 
         </td>
2102 
          <td>
2103 
 
2104 
 
2105 
            <center>SYS</center>
2106 
 
2107 
         </td>
2108 
          <td>
2109 
 
2110 
 
2111 
            <center>--</center>
2112 
         </td>
2113 
          <td>
2114 
 
2115 
 
2116 
            <center>INT</center>
2117 
         </td>
2118 
         </tr>
2119 
 
2120 
 
2121 
        </tbody>
2122 
 
2123 
      </table>
2124 
 
2125 
                    </center>
2126 
         </td>
2127 
         </tr>
2128 
          <tr>
2129 
         <td>PS/2-compatible mode:&nbsp;</td>
2130 
          <td>
2131 
 
2132 
      <center>
2133 
 
2134 
      <table width="400" border="1" cellpadding="2" cellspacing="0" cols="8">
2135 
         <tbody>
2136 
 
2137 
                        <tr>
2138 
         <td>
2139 
 
2140 
 
2141 
            <center>--</center>
2142 
         </td>
2143 
          <td>
2144 
 
2145 
 
2146 
            <center>XLAT</center>
2147 
         </td>
2148 
          <td>
2149 
 
2150 
 
2151 
            <center>_EN2</center>
2152 
 
2153 
         </td>
2154 
          <td>
2155 
 
2156 
 
2157 
            <center>_EN</center>
2158 
         </td>
2159 
          <td>
2160 
 
2161 
 
2162 
            <center>--</center>
2163 
         </td>
2164 
          <td>
2165 
 
2166 
 
2167 
            <center>SYS</center>
2168 
 
2169 
         </td>
2170 
          <td>
2171 
 
2172 
 
2173 
            <center>INT2</center>
2174 
         </td>
2175 
          <td>
2176 
 
2177 
 
2178 
            <center>INT</center>
2179 
         </td>
2180 
         </tr>
2181 
 
2182 
 
2183 
        </tbody>
2184 
 
2185 
      </table>
2186 
 
2187 
                    </center>
2188 
         </td>
2189 
         </tr>
2190 
 
2191 
  </tbody>
2192 
</table>
2193 
              </center>
2194 
 
2195 
<ul>
2196 
 
2197 
  <ul>
2198 
       <li> INT (Input Buffer Full Interrupt) - When set, IRQ 1 is generated
2199 
   when  data is available in the input buffer.</li>
2200 
 
2201 
       <br>
2202 
        0: IBF Interrupt Disabled - You must poll STATUS&lt;IBF&gt; to read
2203 
 input.              <br>
2204 
        1: IBF Interrupt Enabled - Keyboard driver at software int 0x09 handles
2205 
   input.            <li> SYS (System Flag) - Used to manually set/clear SYS
2206 
   flag in Status register.</li>
2207 
       <br>
2208 
        0: Power-on value - Tells POST to perform power-on tests/initialization.
2209 
             <br>
2210 
 
2211 
        1: BAT code received - Tells POST to perform "warm boot" tests/initiailization.
2212 
              <li> OVR (Inhibit Override) - Overrides keyboard's "inhibit"
2213 
 switch  on older motherboards.</li>
2214 
       <br>
2215 
        0: Inhibit switch enabled - Keyboard inhibited if pin P17 is high.
2216 
     <br>
2217 
        1: Inhibit switch disabled - Keyboard not inhibited even if P17 =
2218 
high.              <li>  _EN (Disable keyboard) - Disables/enables keyboard
2219 
interface.</li>
2220 
       <br>
2221 
 
2222 
        0: Enable - Keyboard interface enabled. <br>
2223 
        1: Disable - All keyboard communication is disabled. <li> PC ("PC
2224 
Mode")    - ???Enables keyboard interface somehow???</li>
2225 
       <br>
2226 
        0: Disable - ??? <br>
2227 
        1: Enable - ??? <li> XLAT (Translate Scan Codes) - Enables/disables
2228 
 translation   to set 1 scan codes.</li>
2229 
 
2230 
       <br>
2231 
        0: Translation disabled - Data appears at input buffer exactly as
2232 
read   from  keyboard <br>
2233 
        1: Translation enabled - Scan codes translated to set 1 before put
2234 
 in  input  buffer <li> INT2 (Mouse Input Buffer Full Interrupt) - When set,
2235 
 IRQ  12 is  generated when mouse data is available.</li>
2236 
       <br>
2237 
        0: Auxillary IBF Interrupt Disabled -&nbsp; <br>
2238 
        1: Auxillary IBF Interrupt Enabled -&nbsp; <li> _EN2 (Disable Mouse)
2239 
  -  Disables/enables  mouse interface.</li>
2240 
 
2241 
       <br>
2242 
        0: Enable - Auxillary PS/2 device interface enabled <br>
2243 
        1: Disable - Auxillary PS/2 device interface disabled
2244 
 
2245 
  </ul>
2246 
 
2247 
</ul>
2248 
 
2249 
<ul>
2250 
     <li> ?0x90-0x9F (Write to output port) - Writes command's lower nibble
2251 
   to lower nibble of output port (see Output Port definition.)</li>
2252 
     <li> ?0xA1 (Get version number) - Returns firmware version number.</li>
2253 
 
2254 
     <li> ?0xA4 (Get password) - Returns 0xFA if password exists; otherwise,
2255 
    0xF1.</li>
2256 
     <li> ?0xA5 (Set password) - Set the new password by sending a null-terminated
2257 
    string of scan codes as this command's parameter.</li>
2258 
     <li> ?0xA6 (Check password) - Compares keyboard input with current password.</li>
2259 
     <li> 0xA7 (Disable mouse interface) - PS/2 mode only.&nbsp; Similar
2260 
 to   "Disable keyboard interface" (0xAD) command.</li>
2261 
 
2262 
     <li> 0xA8 (Enable mouse interface) - PS/2 mode only.&nbsp; Similar to
2263 
  "Enable  keyboard interface" (0xAE) command.</li>
2264 
     <li> 0xA9 (Mouse interface test) - Returns 0x00 if okay, 0x01 if Clock
2265 
   line stuck low, 0x02 if clock line stuck high, 0x03 if data line stuck
2266 
low,   and 0x04 if data line stuck high.</li>
2267 
     <li> 0xAA (Controller self-test) - Returns 0x55 if okay.</li>
2268 
     <li> 0xAB (Keyboard interface test) - Returns 0x00 if okay, 0x01 if
2269 
 Clock   line stuck low, 0x02 if clock line stuck high, 0x03 if data line
2270 
stuck  low,   and 0x04 if data line stuck high.</li>
2271 
 
2272 
     <li> 0xAD (Disable keyboard interface) - Sets bit 4 of command byte
2273 
 and   disables all communication with keyboard.</li>
2274 
     <li> 0xAE (Enable keyboard interface) - Clears bit 4 of command byte
2275 
 and  re-enables communication with keyboard.</li>
2276 
     <li> 0xAF (Get version)</li>
2277 
     <li> 0xC0 (Read input port) - Returns values on input port (see Input
2278 
   Port definition.)</li>
2279 
     <li> 0xC1 (Copy input port LSn) - PS/2 mode only. Copy input port's
2280 
 low   nibble to Status register (see Input Port definition)</li>
2281 
 
2282 
     <li> 0xC2 (Copy input port MSn) - PS/2 mode only. Copy input port's
2283 
 high   nibble to Status register (see Input Port definition.)</li>
2284 
     <li> 0xD0 (Read output port) - Returns values on output port (see Output
2285 
    Port definition.)&nbsp;</li>
2286 
     <li> 0xD1 (Write output port) - Write parameter to output port (see
2287 
 Output   Port definition.)</li>
2288 
     <li> 0xD2 (Write keyboard buffer) - Parameter written to input buffer
2289 
   as if received from keyboard.</li>
2290 
     <li> 0xD3 (Write mouse buffer) - Parameter written to input buffer as
2291 
  if received from mouse.</li>
2292 
 
2293 
     <li> 0xD4 (Write mouse Device) - Sends parameter to the auxillary PS/2
2294 
   device.</li>
2295 
     <li> 0xE0 (Read test port) - Returns values on test port (see Test Port
2296 
   definition.)</li>
2297 
     <li> 0xF0-0xFF (Pulse output port) - Pulses command's lower nibble onto
2298 
   lower nibble of output port (see Output Port definition.)</li>
2299 
 
2300 
</ul>
2301 
 
2302 
<p><br>
2303 
              <i>Modern Keyboard Controllers:</i> </p>
2304 
 
2305 
 
2306 
<p>So far, I've only discussed the 8042 keyboard controller.&nbsp; Although
2307 
 modern keyboard controllers remain compatible with the original device, compatibility
2308 
 is their only requirement (and their goal.) </p>
2309 
 
2310 
<p>My motherboard's keyboard controller is a great example of this.&nbsp;
2311 
    I connected a microcontroller+LCD in parallel to my keyboard to see what
2312 
   data is sent by the keyboard controller.&nbsp; At power-up, the keyboard
2313 
  controller sent the "Set LED state" command to turn off all LEDs, then reads
2314 
  the keyboard's ID.&nbsp; When I tried writing data to the output buffer,
2315 
 I found the keyboard controller only forwards the "Set LED state" command
2316 
 and "Set Typematic Rate/Delay" command.&nbsp; It does not allow any other
2317 
 commands to be sent to the keyboard.&nbsp; However, it does emulate the
2318 
keyboard's   response by placing "acknowledge" (0xFA) in the input buffer
2319 
when appropriate   (or 0xEE in response to the "Echo" command.)&nbsp; Furthermore,
2320 
if the keyboard   sends it an erroneous byte, the keyboard controller takes
2321 
care of error handling  (sends the "Retry" command; if byte still erroneous;
2322 
sends error code to keyboard and places error code in input buffer.) </p>
2323 
 
2324 
 
2325 
<p>Once again, keep in mind chipset designers are more interested in   compatibility
2326 
 than standardization.&nbsp; </p>
2327 
 
2328 
<p><b>Initialization:</b> </p>
2329 
 
2330 
<p>The following is the communication between my computer and keyboard
2331 
when it boots-up.&nbsp; I beleive the first three commands were initiated
2332 
    by the keyboad controller, the next command (which enables Num lock LED)
2333 
   was sent by the BIOS, then the rest of the commands were sent my the OS
2334 
 (Win98SE).&nbsp;  Remember, these results are specific to my computer, but
2335 
 it should give you  a general idea as to what happens at startup. </p>
2336 
 
2337 
<blockquote><tt>Keyboard: AA&nbsp; Self-test passed&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
2338 
    ;Keyboard controller init</tt> <br>
2339 
 
2340 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; ED&nbsp; Set/Reset Status
2341 
 Indicators&nbsp;</tt>            <br>
2342 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2343 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; 00&nbsp; Turn off all LEDs</tt>
2344 
            <br>
2345 
 
2346 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2347 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; F2&nbsp; Read ID</tt> <br>
2348 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2349 
 
2350 
                <tt>Keyboard: AB&nbsp; First byte of ID</tt> <br>
2351 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; ED&nbsp; Set/Reset Status
2352 
 Indicators&nbsp;&nbsp;&nbsp;&nbsp;    ;BIOS init</tt> <br>
2353 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2354 
 
2355 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; 02&nbsp; Turn on Num Lock
2356 
 LED</tt>            <br>
2357 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2358 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; F3&nbsp; Set Typematic
2359 
Rate/Delay&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;     ;Windows init</tt>
2360 
 
2361 
  <br>
2362 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2363 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; 20&nbsp; 500 ms / 30.0
2364 
reports/sec</tt>             <br>
2365 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2366 
 
2367 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; F4&nbsp; Enable</tt> <br>
2368 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2369 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; F3&nbsp; Set Typematic
2370 
Rate/delay</tt>             <br>
2371 
 
2372 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt> <br>
2373 
                <tt>Host:&nbsp;&nbsp;&nbsp;&nbsp; 00&nbsp; 250 ms / 30.0
2374 
reports/sec</tt>             <br>
2375 
                <tt>Keyboard: FA&nbsp; Acknowledge</tt></blockquote>
2376 
 
2377 
     <br>
2378 
 <br>
2379 
 
2380 
</body></html>

powered by: WebSVN 2.1.0

© copyright 1999-2024 OpenCores.org, equivalent to Oliscience, all rights reserved. OpenCores®, registered trademark.