Please can you explain me this font 8X8 row and col adress

michael 1978 said:

hi

can somebody explain me, how does work this
[5:0] char_row = row_addr[8:3];
[2:0] font_row = row_addr[2:0]; //char row 8x8
[6:0] char_col = col_addr[9:3];
[2:0] font_col = col_addr[2:0]; // char col 8x8

this 8X8 font but the address [8:3] for row and adress for col [9:3], what does do this bit 4 in row and column
thnx

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Wiljan said:

You are not mention the surrounding circuit so it's a bit hard do know what you want to obtain, but try to have a look here this is a good explanation of how a font are used for VGA

https://www.fpga4fun.com/GraphicLCDpanel4.html

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michael 1978 said:

hello
i just dont understand the
wire [3:0] LCDdata = CounterX[0] ? raster8[7:4] : raster8[3:0]; raster8[7:4] the bit 4(5) is the ram character?

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ecause my LCD panel takes 4-pixels per clock, we need 2 clocks for 1 character width (1 character width=8 pixels). That's why "Character RAM" uses "CounterX[6:1]" instead of "CounterX[5:0]" above.

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ads-ee said:

This is a mux with the lower bit of CounterX being the select which is what the text above it describes

So for 8-pixels you need 2 clocks. I'm assuming the raster8 contains the pixels and the LCD takes 4-bit data, so hence the mux. Selecting between the raster[7:4] and then raster8[3:0].

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Wiljan said:

You will need to tell the FONT look-up ROM what character to show eg A,B,C....(ASCII) and what Row (Line) and Column(Pixel)
To make it a bit more easy to use you will typical write your text to a RAM with the message to show like (Hello World)
So you will also need to tell the RAM what output position you message you want to send to your FONT ROM

There are many FPGA VGA examples on the web like here:
https://opencores.org/projects?expanded=Video%20controller

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