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//////////////////////////////////////////////////////////////////////////////////
// Engineer: Agner Fog
//
// Create Date:    2020-06-22
// Last modified:  2020-06-29
// Module Name:    decoder
// Project Name:   ForwardCom soft core
// Target Devices: Artix 7
// Tool Versions:  Vivado v. 2020.1
// License:        CERN-OHL-W v. 2 or later
// Description:    Driver for LCD displays
// Two LCD displays with each 4 lines x 20 characters
//////////////////////////////////////////////////////////////////////////////////
 
`include "defines.vh"
 
module lcd
  #(parameter numrows = 8,               // number of lines of combined displays (2 - 8)
    parameter numcolumns = 20,           // number of characters per line
    parameter rows_per_display = 4)      // number of rows per display unit
 (input       clock,                     // system clock 100 MHz
  input       reset,                     // reset and clear
  input [4:0] x,                         // column number (0 = left)
  input [2:0] y,                         // row number (0 = top)
  input [7:0] text[0:numcolumns-1],      // text for one line
  input [4:0] text_length,               // length of text
  input       start,                     // start writing
  input       eol,                       // pad with spaces until end of line
  output reg  lcd_rs,                    // LCD RS pin
        output reg  [1:0] lcd_e,               // enable pins for two LCD displays
        output reg  [3:0] lcd_data,            // LCD data, 4 bit bus
        output reg  ready                      // finished writing. ready for next line
);
 
localparam count_bits = 14;              // number of bits in clock divider counter
localparam count_max = (2**count_bits)-1;// maximum count
 
logic [7:0] rowaddress;                  // command for setting row address
reg [count_bits-1:0] counter = 0;        // clock divider
reg [7:0] delay;                         // delay counter
reg [3:0] state = 0;                     // state machine for initialization
                                         // 0  -  9: initialization sequence
                                         // 10 - 11: set x,y position
                                         // 12 - 13: write characters
                                         // 15:      finished
reg [7:0] text_buffer [0:numcolumns-1];  // copy of input text
reg [4:0] column;                        // text column
reg [2:0] row;                           // text row
reg [4:0] text_count;                    // count down characters in text
reg       eol_save;                      // copy of eol
 
/* initialization sequence:
The display can receive data in 4-bit or 8-bit mode. We are using 4-bit mode,
sending 4 bits at a time, with only the upper four bits connected.
First, we send 8'H3x three times to get into 8-bit mode. Then 8'H2x to get
into 4-bit mode. The remaining numbers are 8-bit pairs:
8'H28: multi-line mode (the first needs a long delay)
8'H01: reset (needs long delay)
8'H0C: display on, no cursor, no blink
//8'H06 forward direction
*/
reg [3:0] initialization_sequence [10] = {3, 3, 3, 2, 2, 8, 0, 1, 0, 12 };
 
always_comb begin
    // command to set row address
    if (rows_per_display == 4) begin
        case (row[1:0]) // 4 lines per display
        0: rowaddress = 8'H80 + column;
        1: rowaddress = 8'HC0 + column;
        2: rowaddress = 8'H80 + numcolumns + column;
        3: rowaddress = 8'HC0 + numcolumns + column;
        endcase
    end else begin
        case (row[0])   // 2 lines per display
        0: rowaddress = 8'H80 + column;
        1: rowaddress = 8'HC0 + column;
        endcase
    end
end
 
always_ff @(posedge clock) begin
    lcd_e <= 0;
 
    if (reset) begin
        // reset
        counter <= 0;
        delay <= 8'H80;
        state <= 0;
 
    end else if (start && state == 15) begin
        // write command received
        text_buffer <= text;
        column <= x;
        row <= y;
        text_count <= text_length;
        eol_save <= eol;
        counter <= 0;
        state <= 10;
 
    end else begin
        counter <= counter + 1; // 2**count_bits / 100MHz = 160 �s
        if (state < 10) begin
 
            // initialization sequence
            lcd_rs <= 0;
            if (delay > 0) begin
                if (counter == count_max) delay <= delay - 1;
            end else begin
                lcd_data <= initialization_sequence[state];
                lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse for display unit 0
                lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse for display unit 1
                if (counter == count_max) begin
                    if (state == 9) state <= 15; // finished
                    else state <= state + 1;     // next state
                    delay <= 8'H10;
                end
            end
 
        end else if (state < 12) begin
 
            // set (x,y) position
            lcd_rs <= 0;
            if (delay > 0) begin
                if (counter == count_max) delay <= delay - 1;
            end else begin
                lcd_data <= ~state[0] ? rowaddress[7:4] : rowaddress[3:0];
                if (row < rows_per_display)
                     lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                if (counter == count_max) begin
                    state <= state + 1;
                    delay <= 8'H10;
                end
            end
 
        end else if (state < 15) begin
 
            // write characters
            lcd_rs <= 1;
            if (delay > 0) begin
                if (counter == count_max) delay <= delay - 1;
            end else begin
                if (text_count > 0) begin
                    // write character
                    lcd_data <= ~state[0] ? text_buffer[0][7:4] : text_buffer[0][3:0];
                    if (row < rows_per_display)
                         lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                    else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                end else if (eol_save) begin
                    lcd_data <= ~state[0] ? 2 : 0;                                // write space
                    if (row < rows_per_display)
                         lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                    else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse
                end
 
                if (counter == count_max) begin
                    if (state[0]) begin
                        column <= column + 1;                                     // count up column index
                        if (text_count != 0) text_count <= text_count - 1;        // count down number of characters
                        for (int i = 0; i < numcolumns-1; i++) begin
                            text_buffer[i] <= text_buffer[i+1];                   // shift down to get next character
                        end
                    end
                    if (state[0] && (column == numcolumns-1 || (text_count == 0 && !eol_save))) begin
                        state <= 15;                                              // finished
                    end else begin
                        state[0] <= ~state[0];
                    end
                    // delay <= 8'H01;
                end
            end
        end else begin
            // state = 15. finished
            lcd_e <= 0;
        end
    end
    if (state == 15) ready <= 1;
    else ready <= 0;
 
end
 
 
endmodule

Line No.	Rev	Author	Line
1	4	Agner	`//////////////////////////////////////////////////////////////////////////////////`
2			`// Engineer: Agner Fog`
3			`//`
4			`// Create Date: 2020-06-22`
5			`// Last modified: 2020-06-29`
6			`// Module Name: decoder`
7			`// Project Name: ForwardCom soft core`
8			`// Target Devices: Artix 7`
9			`// Tool Versions: Vivado v. 2020.1`
10			`// License: CERN-OHL-W v. 2 or later`
11			`// Description: Driver for LCD displays`
12			`// Two LCD displays with each 4 lines x 20 characters`
13			`//////////////////////////////////////////////////////////////////////////////////`
14
15			`include "defines.vh"
16
17			`module lcd`
18			`#(parameter numrows = 8, // number of lines of combined displays (2 - 8)`
19			`parameter numcolumns = 20, // number of characters per line`
20			`parameter rows_per_display = 4) // number of rows per display unit`
21			`(input clock, // system clock 100 MHz`
22			`input reset, // reset and clear`
23			`input [4:0] x, // column number (0 = left)`
24			`input [2:0] y, // row number (0 = top)`
25			`input [7:0] text[0:numcolumns-1], // text for one line`
26			`input [4:0] text_length, // length of text`
27			`input start, // start writing`
28			`input eol, // pad with spaces until end of line`
29			`output reg lcd_rs, // LCD RS pin`
30			`output reg [1:0] lcd_e, // enable pins for two LCD displays`
31			`output reg [3:0] lcd_data, // LCD data, 4 bit bus`
32			`output reg ready // finished writing. ready for next line`
33			`);`
34
35			`localparam count_bits = 14; // number of bits in clock divider counter`
36			`localparam count_max = (2**count_bits)-1;// maximum count`
37
38			`logic [7:0] rowaddress; // command for setting row address`
39			`reg [count_bits-1:0] counter = 0; // clock divider`
40			`reg [7:0] delay; // delay counter`
41			`reg [3:0] state = 0; // state machine for initialization`
42			`// 0 - 9: initialization sequence`
43			`// 10 - 11: set x,y position`
44			`// 12 - 13: write characters`
45			`// 15: finished`
46			`reg [7:0] text_buffer [0:numcolumns-1]; // copy of input text`
47			`reg [4:0] column; // text column`
48			`reg [2:0] row; // text row`
49			`reg [4:0] text_count; // count down characters in text`
50			`reg eol_save; // copy of eol`
51
52			`/* initialization sequence:`
53			`The display can receive data in 4-bit or 8-bit mode. We are using 4-bit mode,`
54			`sending 4 bits at a time, with only the upper four bits connected.`
55			`First, we send 8'H3x three times to get into 8-bit mode. Then 8'H2x to get`
56			`into 4-bit mode. The remaining numbers are 8-bit pairs:`
57			`8'H28: multi-line mode (the first needs a long delay)`
58			`8'H01: reset (needs long delay)`
59			`8'H0C: display on, no cursor, no blink`
60			`//8'H06 forward direction`
61			`*/`
62			`reg [3:0] initialization_sequence [10] = {3, 3, 3, 2, 2, 8, 0, 1, 0, 12 };`
63
64			`always_comb begin`
65			`// command to set row address`
66			`if (rows_per_display == 4) begin`
67			`case (row[1:0]) // 4 lines per display`
68			`0: rowaddress = 8'H80 + column;`
69			`1: rowaddress = 8'HC0 + column;`
70			`2: rowaddress = 8'H80 + numcolumns + column;`
71			`3: rowaddress = 8'HC0 + numcolumns + column;`
72			`endcase`
73			`end else begin`
74			`case (row[0]) // 2 lines per display`
75			`0: rowaddress = 8'H80 + column;`
76			`1: rowaddress = 8'HC0 + column;`
77			`endcase`
78			`end`
79			`end`
80
81			`always_ff @(posedge clock) begin`
82			`lcd_e <= 0;`
83
84			`if (reset) begin`
85			`// reset`
86			`counter <= 0;`
87			`delay <= 8'H80;`
88			`state <= 0;`
89
90			`end else if (start && state == 15) begin`
91			`// write command received`
92			`text_buffer <= text;`
93			`column <= x;`
94			`row <= y;`
95			`text_count <= text_length;`
96			`eol_save <= eol;`
97			`counter <= 0;`
98			`state <= 10;`
99
100			`end else begin`
101			`counter <= counter + 1; // 2**count_bits / 100MHz = 160 �s`
102			`if (state < 10) begin`
103
104			`// initialization sequence`
105			`lcd_rs <= 0;`
106			`if (delay > 0) begin`
107			`if (counter == count_max) delay <= delay - 1;`
108			`end else begin`
109			`lcd_data <= initialization_sequence[state];`
110			`lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse for display unit 0`
111			`lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse for display unit 1`
112			`if (counter == count_max) begin`
113			`if (state == 9) state <= 15; // finished`
114			`else state <= state + 1; // next state`
115			`delay <= 8'H10;`
116			`end`
117			`end`
118
119			`end else if (state < 12) begin`
120
121			`// set (x,y) position`
122			`lcd_rs <= 0;`
123			`if (delay > 0) begin`
124			`if (counter == count_max) delay <= delay - 1;`
125			`end else begin`
126			`lcd_data <= ~state[0] ? rowaddress[7:4] : rowaddress[3:0];`
127			`if (row < rows_per_display)`
128			`lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
129			`else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
130			`if (counter == count_max) begin`
131			`state <= state + 1;`
132			`delay <= 8'H10;`
133			`end`
134			`end`
135
136			`end else if (state < 15) begin`
137
138			`// write characters`
139			`lcd_rs <= 1;`
140			`if (delay > 0) begin`
141			`if (counter == count_max) delay <= delay - 1;`
142			`end else begin`
143			`if (text_count > 0) begin`
144			`// write character`
145			`lcd_data <= ~state[0] ? text_buffer[0][7:4] : text_buffer[0][3:0];`
146			`if (row < rows_per_display)`
147			`lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
148			`else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
149			`end else if (eol_save) begin`
150			`lcd_data <= ~state[0] ? 2 : 0; // write space`
151			`if (row < rows_per_display)`
152			`lcd_e[0] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
153			`else lcd_e[1] <= counter[count_bits-1:count_bits-2] == 2'b01; // generate pulse`
154			`end`
155
156			`if (counter == count_max) begin`
157			`if (state[0]) begin`
158			`column <= column + 1; // count up column index`
159			`if (text_count != 0) text_count <= text_count - 1; // count down number of characters`
160			`for (int i = 0; i < numcolumns-1; i++) begin`
161			`text_buffer[i] <= text_buffer[i+1]; // shift down to get next character`
162			`end`
163			`end`
164			`if (state[0] && (column == numcolumns-1 \|\| (text_count == 0 && !eol_save))) begin`
165			`state <= 15; // finished`
166			`end else begin`
167			`state[0] <= ~state[0];`
168			`end`
169			`// delay <= 8'H01;`
170			`end`
171			`end`
172			`end else begin`
173			`// state = 15. finished`
174			`lcd_e <= 0;`
175			`end`
176			`end`
177			`if (state == 15) ready <= 1;`
178			`else ready <= 0;`
179
180			`end`
181
182
183			`endmodule`

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