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[/] [System09/] [rev_86/] [src/] [upld/] [upld_cf8.asm] - Blame information for rev 150

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Line No. Rev Author Line
1 59 davidgb
*
2
** FLEX 9 DISK DRIVERS
3
*
4
* FOR SYS09BUG ON THE DIGILENT SPARTAN 3 STARTER BOARD
5
* WITH I/O MAPPED AT $XE000
6
* AND ROM MAPPED AT $XF000
7
* THE DIGILENT SPARTAN 3 STARTER BOARD HAS 1MBYTE OF SRAM
8
* THE FIRST 64K IS USED BY FLEX,
9
* THE SECOND 128K IS USED AS A ROM DISK
10
* THE REMAINING RAM IS USED FOR A RAM DISK
11
*
12
*
13
CFLAG   EQU $01     CARRY FLAG
14
VFLAG   EQU $02     OVERFLOW FLAG
15
ZFLAG   EQU $04     ZERO FLAG
16
NFLAG   EQU $08     NEGATIVE FLAG
17
IFLAG   EQU $10     IRQ MASK CC
18
HFLAG   EQU $20     HALF CARRY
19
FFLAG   EQU $40     FIRQ MASK CC
20
EFLAG   EQU $80     ENTIRE FLAG
21
*
22
MAPPAG  EQU $00     PAGE $0000 DAT ADDRESS
23
*
24
* Serial Port
25
*
26
ACIAS   EQU $E000
27
ACIAC1  EQU ACIAS
28
ACIAD1  EQU ACIAS+1
29
DELCON  EQU 1250    Delay (Processor clock in MHz * 50)
30
*
31
* XMODEM Control characters
32
*
33
SOH     EQU $01
34
EOT     EQU $04
35
ACK     EQU $06
36
NAK     EQU $15
37
CAN     EQU $18
38
*
39
* Some dummy Constants
40
*
41
RMAXTRK EQU 48
42
RMAXSEC EQU 14
43
RTOTSEC EQU RMAXTRK*RMAXSEC-RMAXSEC
44
*
45
* Start
46
*
47
        ORG $0100
48
START   LBSR  UXSUB
49
        JMP  [$F800]  Jump to monitor on Completion.
50
*
51
*
52
* RAM SPACE
53
*
54
DRVNUM  FCB  0
55
TRACK   FCB  0
56
SECTOR  FCB  0
57
CHKSUM  FCB  0
58
BLKNUM  FCB  0 Xmodem block number
59
BYTCNT  FCB  0 Xmodem byte count
60
XSTATE  FDB  0 Xmodem State Vector
61
DELCNT  FCB  $00,$00,$00 Xmodem Poll timer
62
MAXTRK  FCB  0
63
MAXSEC  FCB  0
64
        ORG  $0200
65
*
66
* SECTOR BUFFER
67
*
68
BUFFER  RMB  256
69
*
70
* ACIA INPUT TEST
71
*
72
INTEST  LDA ACIAC1
73
        BITA #$01
74
        RTS
75
*
76
* RESET ACIA
77
*
78
ACIRST  LDA #$03 master reset
79
        STA  ACIAC1
80
        LDA #$11
81
        STA ACIAC1
82
        RTS
83
*
84
* ACIA INPUT
85
*
86
INTER   LDA  #16
87
        STA  DELCNT+0
88
        CLR  DELCNT+1
89
        CLR  DELCNT+2
90
INTER0  LDA  ACIAC1
91
        BITA #$01
92
        BNE  INTER1
93
        BITA #$78
94
        BEQ  INTER2
95
        BSR  ACIRST
96
        BRA  INTER
97
*
98
INTER1  LDA  ACIAD1
99
        ANDCC #$FF-VFLAG
100
        RTS
101
*
102
INTER2  DEC  DELCNT+2
103
        BNE  INTER0
104
        DEC  DELCNT+1
105
        BNE  INTER0
106
        DEC  DELCNT+0
107
        BNE  INTER0
108
        CLRA
109
        ORCC #VFLAG
110
        RTS
111
*
112
* ACIA OUTPUT
113
*
114
OUTTER  PSHS A
115
*
116
OUTTE1  LDA ACIAC1
117
        BITA #$02
118
        BNE  OUTTE2
119
        BITA #$78
120
        BEQ  OUTTE1
121
        BSR  ACIRST
122
        BRA  OUTTE1
123
*
124
OUTTE2  PULS A
125
        STA ACIAD1
126
        RTS
127
*
128
* Print Data
129
*
130
PDATA0  BSR  OUTTER
131
PDATA1  LDA  ,X+
132
        CMPA #$04
133
        BNE  PDATA0
134
        RTS
135
*
136
** 'UX' Xmodem ROM Disk upload
137
*
138
UXMES0  FCB $0D,$0A
139
        FCC 'Xmodem ROM Disk Upload'
140
        FCB 4
141
UXMES1  FCB $0D,$0A
142
        FCC 'Upload Complete'
143
        FCB 4
144
UXMES2  FCB $0D,$0A
145
        FCC 'Upload Error'
146
        FCB 4
147
UXMSG3  FCB $0D,$0A
148
        FCC 'Drive Number :'
149
        FCB 4
150
UXMSG4  FCB $0D,$0A
151
        FCC 'Are You Sure ? (Y/N)'
152
        FCB 4
153
*
154
* Print Banner
155
*
156
UXSUB   LDX #UXMES0
157
        LBSR PDATA1
158
*
159
* Prompt for Disk drive number (0 to 3)
160
*
161
        LDX #UXMSG3
162
        LBSR PDATA1
163
UXSUB1  LBSR INTER
164
        BVS  UXSUB1
165
        LBSR OUTTER
166
        CMPA #'0
167
        LBLO UXEXIT
168
        CMPA #'3
169
        LBHI UXEXIT
170
        SUBA #'0
171
        STA  DRVNUM
172
*
173
* Report selected drive
174
*
175
        LDX #UXMSG3
176
        LBSR PDATA1
177
        LDA  DRVNUM
178
        ADDA #'0
179
        LBSR OUTTER
180
*
181
* Ask for confirmation (Y/N)
182
*
183
        LDX #UXMSG4
184
        LBSR PDATA1
185
UXSUB2  LBSR INTER
186
        BVS  UXSUB2
187
        LBSR OUTTER
188
        ANDA #$5F
189
        CMPA #'N
190
        LBEQ UXEXIT
191
        CMPA #'Y
192
        BNE  UXSUB
193
*
194
* We have confirmation ... now load the disk image
195
*
196
        LBSR INITDR
197
        LDU  #XSTST
198
        STU  XSTATE
199
        LDA  #1
200
        STA  BLKNUM
201
*
202
* Sector1
203
*
204
        LDX  #BUFFER
205
*
206
        CLRA         TRACK 0
207
        LDB  #$01    SECTOR 1
208
        STA  TRACK
209
        STB  SECTOR
210
*
211
        LBSR XREAD
212
        LBCS UXERR
213
        LBSR XACK
214
        LBSR XREAD
215
        LBCS UXERR
216
*
217
        LDX  #BUFFER
218
        LDA  TRACK
219
        LDB  SECTOR
220
        LBSR WRITSC
221
        LBSR XACK
222
*
223
* Sector 2
224
*
225
        LDX  #BUFFER
226
*
227
        LDA  TRACK
228
        LDB  SECTOR
229
        INCB
230
        STA  TRACK
231
        STB  SECTOR
232
*
233
        LBSR XREAD
234
        LBCS UXERR
235
        LBSR XACK
236
        LBSR XREAD
237
        LBCS UXERR
238
*
239
        LDX  #BUFFER
240
        LDA  TRACK
241
        LDB  SECTOR
242
        LBSR WRITSC
243
*
244
        LBSR XACK
245
*
246
* Sector 3 - SIR
247
*
248
        LDX  #BUFFER
249
*
250
        LDA  TRACK
251
        LDB  SECTOR
252
        INCB
253
        STA  TRACK
254
        STB  SECTOR
255
*
256
        LBSR XREAD
257
        LBCS UXERR
258
        LBSR XACK
259
        LBSR XREAD
260
        LBCS UXERR
261
*
262
        LDX  #BUFFER
263
        LDA  38,X
264
        INCA
265
        STA  MAXTRK
266
        LDB  39,X
267
        INCB
268
        STB  MAXSEC
269
        LDA  TRACK
270
        LDB  SECTOR
271
        LBSR WRITSC
272
*
273
        LBSR XACK
274
*
275
* Sector 4 to Last Track & Sector
276
*
277
*
278
        LDA  TRACK
279
        LDB  SECTOR
280
        INCB
281
*
282
UXLOOP  LDX  #BUFFER
283
        STA  TRACK
284
        STB  SECTOR
285
*
286
        LBSR XREAD
287
        LBCS UXERR
288
        LBSR XACK
289
        LBSR XREAD
290
        LBCS UXERR
291
*
292
        LDX  #BUFFER
293
        LDA  TRACK
294
        LDB  SECTOR
295
        LBSR WRITSC
296
        LBSR XACK
297
*
298
        LDA  TRACK
299
        LDB  SECTOR
300
        INCB
301
        CMPB MAXSEC
302
        BNE  UXLOOP
303
        LDB  #1
304
        INCA
305
        CMPA MAXTRK
306
        BNE  UXLOOP
307
*
308
*
309
*  Write Boot sector
310
*
311
        LDX  #$C000
312
        CLRA         TRACK 0
313
        LDB  #$01    SECTOR 1
314
        STA  TRACK
315
        STB  SECTOR
316
        LBSR WRITSC
317
*
318
UXEXIT  LDX  #UXMES1
319
        JMP  PDATA1
320
*
321
UXERR   LDX  #UXMES2
322
        LBRA PDATA1
323
*
324
* Get a Byte using XModem protocol
325
* Carry clear => no errors
326
* Carry set   => errors
327
*
328
XREAD   PSHS U
329
        LDU  XSTATE
330
*
331
XBYTE0  LBSR INTER
332
        BVC  XBYTE1
333
        LDA  #NAK
334
        LBSR OUTTER
335
        LDU  #XSTST
336
        BRA  XBYTE0
337
*
338
XBYTE1  JSR  ,U
339
        BNE  XBYTE0
340
        STU  XSTATE
341
        PULS U,PC
342
*
343
* START - LOOK FOR SOH (START OF HEADER) = $01
344
*
345
XSTST   CMPA #SOH
346
        BNE  XSTST1
347
        LDU  #XSTBL
348
        ANDCC #$FF-CFLAG-ZFLAG No abort, no valid data (no exit)
349
        RTS
350
*
351
XSTST1  CMPA #EOT
352
        BNE  XSTST2
353
        LDA  #ACK
354
        LBSR OUTTER
355
        ORCC  #CFLAG+ZFLAG  Set (c)=1 abort & exit
356
        RTS
357
*
358
XSTST2  CMPA #CAN
359
        BNE  XSTST3
360
        ORCC  #CFLAG+ZFLAG  Set (c)=1 abort & exit
361
        RTS
362
*
363
XSTST3  ANDCC #$FF-CFLAG-ZFLAG
364
        RTS
365
*
366
* Got SOH
367
* Now get block number
368
*
369
XSTBL   CMPA BLKNUM
370
        BNE  XSTBLE
371
        LDU  #XSTCOM
372
        ANDCC #$FF-CFLAG-ZFLAG No abort, No valid data (no exit)
373
        RTS
374
*
375
* Error in block number
376
*
377
XSTBLE  LDA  #NAK
378
        LBSR OUTTER
379
        LDU  #XSTST
380
        ANDCC #$FF-CFLAG-ZFLAG No abort, No valid data (no exit)
381
        RTS
382
*
383
* Get complement of block number
384
*
385
XSTCOM  COMA
386
        CMPA BLKNUM
387
        BNE  XSTBLE
388
        CLR  CHKSUM
389
        LDA  #128
390
        STA  BYTCNT
391
        LDU  #XSTDA
392
        ANDCC #$FF-CFLAG-ZFLAG No abort, No valid data (no exit)
393
        RTS
394
*
395
* Get data bytes
396
*
397
XSTDA   PSHS A
398
        ADDA CHKSUM
399
        STA  CHKSUM
400
        PULS A
401
        DEC  BYTCNT
402
        BNE  XSTDA1
403
        LDU  #XSTCK
404
XSTDA1  STA  ,X+
405
        ANDCC #$FF-CFLAG-ZFLAG No abort, no valid data (no exit)
406
        RTS
407
*
408
* Byte count reached zero
409
* Check checksum byte
410
*
411
XSTCK   CMPA CHKSUM
412
        BNE  XSTCK1 retry if wrong checksum
413
*
414
* Checksum OK ...
415
* increment block number
416
* Don't send ACK until data written to CF
417
*
418
        INC  BLKNUM
419
        LDU  #XSTST
420
        ANDCC #$FF-CFLAG No abort
421
        ORCC #ZFLAG      Valid data (exit)
422
        RTS
423
*
424
* Checksum Error detected ...
425
* Reset Sector counter in ACCB to last 128 byte boundary
426
* and send NAK
427
*
428
XSTCK1  PSHS B
429
        TFR  X,D
430
        DECB
431
        ANDB #128
432
        TFR  D,X
433
        PULS B
434
        LDA  #NAK
435
XSTCK2  LBSR OUTTER
436
        LDU  #XSTST
437
        ANDCC #$FF-CFLAG-ZFLAG No abort, no valid data (no exit)
438
        RTS
439
*
440
* Acknowledge Data Received
441
*
442
XACK    PSHS A
443
        LDA  #ACK
444
        LBSR OUTTER
445
        PULS A,PC
446
*
447
*
448
** FLEX 9 COMPACT FLASH DISK DRIVERS
449
*
450
* FOR SYS09BUG 1.2 ON THE BURCHED B5-X300
451
* WITH I/O MAPPED AT $XE000
452
* AND ROM MAPPED AT $XF000
453
* THE BURCHED B5-X300 HAS 256KBYTES OF SRAM
454
* THE FIRST 64K IS USED BY FLEX,
455
* THE SECOND 192K MAY BE USED AS A RAM DISK
456
*
457
*
458
IMASK  EQU $10     IRQ MASK CC
459
FMASK  EQU $40     FIRQ MASK CC
460
DATREG EQU $FFF0   DAT REGISTERS
461
*
462
CF_BASE    EQU $E040
463
CF_DATA    EQU CF_BASE+0
464
CF_ERROR   EQU CF_BASE+1 ; read error
465
CF_FEATURE EQU CF_BASE+1 ; write feature
466
CF_SCNT    EQU CF_BASE+2
467
CF_SNUM    EQU CF_BASE+3
468
CF_CLO     EQU CF_BASE+4
469
CF_CHI     EQU CF_BASE+5
470
CF_HEAD    EQU CF_BASE+6
471
CF_STATUS  EQU CF_BASE+7 ; read status
472
CF_COMAND  EQU CF_BASE+7 ; write command
473
*
474
* Command Equates
475
*
476
CMDREAD    EQU $20 ; Read Single sector
477
CMDWRITE   EQU $30 ; Write Single sector
478
CMDFEATURE EQU $EF
479
FEAT8BIT   EQU $01 ; enable 8 bit transfers
480
HEADLBA    EQU $E0
481
*
482
* Status bit equates
483
*
484
BSY        EQU $80
485
DRDY       EQU $40
486
DRQ        EQU $08
487
ERR        EQU $01
488
*
489
*
490
* INITIALIZE CF CARD FOR 8 BIT LBA MODE
491
*
492
INITDR BSR WAITRDY
493
       LDA  #HEADLBA
494
       STA  CF_HEAD
495
       LDA #FEAT8BIT
496
       STA CF_FEATURE
497
       LDA #CMDFEATURE
498
       STA CF_COMAND
499
       BRA WAITRDY
500
*
501
* Seek track and sector
502
* A holds track number (0 - ??)
503
* B holds sector number (1 - ??)
504
* Sector numbers starts from 1
505
* subtract 1 to start from sector 0 on CF
506
*
507
SEEKTS DECB
508
       STB  CF_SNUM
509
       STA  CF_CLO
510
       LDB  DRVNUM
511
       STB  CF_CHI
512
       LDB  #$01
513
       STB  CF_SCNT
514
       CLRB
515
       RTS
516
*
517
* READ SECTORS FROM CF
518
*
519
*
520
READSC BSR  SEEKTS
521
       LDA  #CMDREAD ; IDE READ MULTIPLE
522
       STA  CF_COMAND
523
       BSR  WAITRDY
524
*
525
* READ LOOP
526
*
527
       CLRB
528
RDLP1  BSR  WAITDRQ
529
       LDA  CF_DATA
530
       STA  ,X+
531
       DECB
532
       BNE  RDLP1
533
*
534
       CLRB
535
RDLP2  BSR  WAITDRQ
536
       LDA  CF_DATA
537
       DECB
538
       BNE  RDLP2
539
*
540
       BSR  WAITRDY
541
       CLRB
542
       RTS
543
*
544
* WRITE SECTOR TO CF
545
*
546
WRITSC BSR  SEEKTS   ; SEEK TRACK & SECTOR
547
       LDA  #CMDWRITE ; IDE WRITE MULTIPLE
548
       STA  CF_COMAND
549
       BSR  WAITRDY
550
*
551
* WRITE LOOP
552
*
553
       CLRB
554
WRTLP1 BSR  WAITDRQ
555
       LDA  ,X+
556
       STA  CF_DATA
557
       DECB
558
       BNE  WRTLP1
559
*
560
       CLRB
561
WRTLP2 BSR  WAITDRQ
562
       CLRA
563
       STA  CF_DATA
564
       DECB
565
       BNE WRTLP2
566
*
567
       BSR  WAITRDY
568
       CLRB
569
       RTS
570
*
571
* CHECK FOR BUSY
572
* Doubles as VERIFY
573
*
574
BUSY   CLRB            Never busy
575
       RTS
576
*
577
* DRIVE SELECT DISK DRIVER
578
*
579
DRVSEL LDA   3,X       GET DRIVE # FROM FCB
580
       CMPA  #3
581
       BLS   DRVS2     IF > 3, SET IT TO 0
582
       CLRA
583
DRVS2  STA   DRVNUM
584
       CLRB            ; SET Z, CLEAR C
585
       RTS
586
*
587
* CHECK DRIVE READY DISK DRIVER
588
*
589
CHKDRV LDA  3,X
590
       CLRB             ; CLEAR C, SET Z
591
       RTS
592
*
593
* WAIT UNTIL READY
594
*
595
WAITRDY LDA  CF_STATUS
596
        BITA #BSY
597
        BNE  WAITRDY
598
        LDA  CF_STATUS
599
        BITA #DRDY
600
        BEQ  WAITRDY
601
        RTS
602
*
603
* WAIT FOR DATA REQUEST
604
*
605
WAITDRQ LDA  CF_STATUS
606
        BITA #DRQ
607
        BEQ  WAITDRQ
608
        RTS
609
*
610
*******************************************************
611
*
612
* Bootstrap FLEX Loader
613
*
614
* SBUG1.8 loads the bootstap loader at $C000
615
* however the Flex adaption manual has the
616
* bootstrap loader residing at $C100
617
*
618
******************************************************
619
*
620
* Equates
621
*
622
STACK   EQU $C0FF
623
SCTBUF  EQU $C300
624
*
625
* Start of Utility
626
*
627
        ORG $C000
628
BOOT    BRA LOAD0
629
        FCB 0,0,0
630
TRK     FCB 0        File start track
631
SCT     FCB 0        File start sector
632
DNS     FCB 0        Density Flag (not used)
633
TADR    FDB $C000    Transfer address
634
LADR    FDB 0        Load Address
635
DRNUM   FCB 0        Drive number 0
636
*
637
LOAD0   LDS  #STACK   Set up stack
638
        LDD  TRK      Set up start track and sector
639
        STD  SCTBUF
640
        LDY  #SCTBUF+256
641
*
642
* Perform actual file load
643
*
644
LOAD1   BSR GETCH    Get acharcater
645
        CMPA #$02    Data record hearder ?
646
        BEQ  LOAD2   Skip, is so
647
        CMPA #$16    Xfr address hearder ?
648
        BNE LOAD1    Loop if neither
649
*
650
* Get transfer address
651
*
652
        BSR  GETCH
653
        STA  TADR
654
        BSR  GETCH
655
        STA  TADR+1
656
        BRA  LOAD1
657
*
658
* Load data record
659
*
660
LOAD2  BSR  GETCH  Get load address
661
       STA  LADR
662
       BSR  GETCH
663
       STA  LADR+1
664
       BSR  GETCH  Get Bytes count
665
       TFR  A,B
666
       TSTB
667
       BEQ  LOAD1 Loop if count = 0
668
       LDX  LADR  Get load address
669
LOAD3  PSHS B,X
670
       BSR  GETCH  Get data character
671
       PULS B,X
672
       STA  ,X+    Store at load address
673
       DECB
674
       BNE  LOAD3  Loop until count = 0
675
       BRA  LOAD1
676
*
677
* Get Character routine
678
* Reads a sector if needed
679
*
680
GETCH  CMPY #SCTBUF+256 out of data ?
681
       BNE  GETCH4      Go read Character if not
682
GETCH2 LDX  #SCTBUF     Point to buffer
683
       LDD  0,X         Get forward Link
684
       BEQ  GO          if zero, file is loaded
685
       BSR  READ        Read next sector
686
       BNE  BOOT        start over if error
687
       LDY  #SCTBUF+4   Point past link
688
GETCH4 LDA  ,Y+         Else, get a character
689
       RTS
690
*
691
* File is loaded, Jump to it
692
*
693
GO     JMP  [TADR]      Jump to transfer address
694
 
695
*
696
** FLEX 9 COMPACT FLASH DISK DRIVERS
697
*
698
* FOR SYS09BUG 1.2 ON THE BURCHED B5-X300
699
* WITH I/O MAPPED AT $XE000
700
* AND ROM MAPPED AT $XF000
701
* THE BURCHED B5-X300 HAS 256KBYTES OF SRAM
702
* THE FIRST 64K IS USED BY FLEX,
703
* THE SECOND 192K MAY BE USED AS A RAM DISK
704
*
705
*
706
*IMASK  EQU $10     IRQ MASK CC
707
*FMASK  EQU $40     FIRQ MASK CC
708
*DATREG EQU $FFF0   DAT REGISTERS
709
*
710
*CF_BASE    EQU $E040
711
*CF_DATA    EQU CF_BASE+0
712
*CF_ERROR   EQU CF_BASE+1 ; read error
713
*CF_FEATURE EQU CF_BASE+1 ; write feature
714
*CF_SCNT  EQU CF_BASE+2
715
*CF_SNUM  EQU CF_BASE+3
716
*CF_CLO   EQU CF_BASE+4
717
*CF_CHI   EQU CF_BASE+5
718
*CF_HEAD    EQU CF_BASE+6
719
*CF_STATUS  EQU CF_BASE+7 ; read status
720
*CF_COMAND  EQU CF_BASE+7 ; write command
721
*
722
* Command Equates
723
*
724
*CMDREAD    EQU $20 ; Read Single sector
725
*CMDWRITE   EQU $30 ; Write Single sector
726
*CMDFEATURE EQU $EF
727
*FEAT8BIT   EQU $01 ; enable 8 bit transfers
728
*HEADLBA    EQU $E0
729
*
730
* Status bit equates
731
*
732
*BSY        EQU $80
733
*DRDY       EQU $40
734
*DRQ        EQU $08
735
*ERR        EQU $01
736
*
737
* Seek track and sector
738
* A holds track number (0 - ??)
739
* B holds sector number (1 - ??)
740
* Sector numbers starts from 1
741
* subtract 1 to start from sector 0 on CF
742
*
743
SEEK   DECB
744
       STB  CF_SNUM
745
       STA  CF_CLO
746
       LDB  DRNUM
747
       STB  CF_CHI
748
       LDB  #$01
749
       STB  CF_SCNT
750
       CLRB
751
       RTS
752
*
753
* READ SECTORS FROM CF
754
*
755
*
756
READ   BSR  SEEK
757
       LDA  #CMDREAD ; IDE READ MULTIPLE
758
       STA  CF_COMAND
759
       BSR  WTRDY
760
*
761
* READ LOOP
762
*
763
       CLRB
764
READ1  BSR  WTDRQ
765
       LDA  CF_DATA
766
       STA  ,X+
767
       DECB
768
       BNE  READ1
769
*
770
       CLRB
771
READ2  BSR  WTDRQ
772
       LDA  CF_DATA
773
       DECB
774
       BNE  READ2
775
*
776
       BSR  WTRDY
777
       CLRB
778
       RTS
779
*
780
* WAIT UNTIL READY
781
*
782
WTRDY   LDA  CF_STATUS
783
        BITA #BSY
784
        BNE  WTRDY
785
        LDA  CF_STATUS
786
        BITA #DRDY
787
        BEQ  WTRDY
788
        RTS
789
*
790
* WAIT FOR DATA REQUEST
791
*
792
WTDRQ   LDA  CF_STATUS
793
        BITA #DRQ
794
        BEQ  WTDRQ
795
        RTS
796
*
797
       END START

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