Greenbird

The verilog provided at 4.3_psp_lcd can also be used to drive a VGA display. Only the timing and resolution in h_sync, v_sync and in_picture and the pixel clock in clk should be changed to the correct values as explained in vga_timing.

Example for 640x480

in_picture module

Change the values of the front and backporch in in_picture by changing

C: in_picture

1 2 3

assign h_pixel = h_addr - 10'h30; assign v_line = v_addr - 9'h10; assign in_picture = (h_addr > 10'h30 && h_addr < 10'h213 && v_addr > 9'h10 && v_addr < 9'h120)?1'b1:1'b0;

to

C: in_picture

1 2 3

assign h_pixel = h_addr - 10'h90; assign v_line = v_addr - 9'h23; assign in_picture = (h_addr > 10'h90 && h_addr < 10'h310 && v_addr > 9'h23 && v_addr < 9'h1E2)?1'b1:1'b0;

clk module

Change the pixel clock in clk by changing

C: clk

1 2 3 4 5 6 7 8 9

always @ (posedge clk_50MHz) begin if (count == 3'h5) count <= 0; else count <= count + 3'h1; end assign clk_9MHz = count[2];

to

C: clk

1 2 3 4

always @ (posedge clk_50MHz) count <= ~count; assign clk_9MHz = count[0];

v_sync module

In v_sync module, change the sync pulse duration by changing the following:

C: v_sync

1 2 3 4 5 6 7

if (count == 286) count <= 9'h0; if (count < 12) sync <= 1'h0; else sync <= 1'h1;

to

C: v_sync

1 2 3 4 5 6 7

if (count == 525) count <= 9'h0; if (count < 2) sync <= 1'h0; else sync <= 1'h1;

h_sync module

In h_sync module, change the sync pulse duration by changing the following:

C: h_sync

1 2 3 4 5 6 7

if (count == 525) //525 count <= 10'h0; if (count < 45) //45 sync <= 1'h0; else sync <= 1'h1;

to

C: h_sync

1 2 3 4 5 6 7

if (count == 799) count <= 10'h0; if (count < 96) sync <= 1'h0; else sync <= 1'h1;

Signal widths

Also, the width of h_addr, v_addr, h_pixel, v_line and address should be changed and the depth of the display memory

	old	new
h_addr	10	11
v_addr	9	10
h_pixel	10	11
v_line	9	10
address	10	11
memory depth	2048	4096

Result

This will result in a display memory of 128×32 character with 30×80 visible character at a resolution of 680×480 (60 Hz refresh rate). It will use up 64 kB (70%) of the available ram bits. It is recommended to reduce the font table to 64 characters and (if needed) to increase to size of the characters to 16×32 instead of 8×16. This is done by shifting the h_addr and v_addr lines one to the left and increasing the shift register (in the color module) every other clock cycle.