Character Map with Xilinx FPGA

[usenet]

Hello,

I'm trying to display text via the vga port of my xilinx spartan-3. The
question is how do I do it. I now that I have to generate a character-map or
a character rom. But has some one experience with this, i.e. some vhdl code,
and how do I do this with modelsim.

I already searched with google and either I'm too dumb or there is nothing
helpful out there. So how do I code the characters into vhdl with modelsim
so that it will be synthesized on a spartan-3. Has someone a coding example?

Thanks in advance

 

[Martin Thompson]

Hello,

I'm trying to display text via the vga port of my xilinx spartan-3. The
question is how do I do it. I now that I have to generate a character-map or
a character rom. But has some one experience with this, i.e. some vhdl code,
and how do I do this with modelsim.

Do you have the bitmaps you want to use?
Assuming they are simple 8 bit wide characters with the same number of
rows (let's say 8 for this exambple) in each you can do:
constant char_rom : integer range 0 to 255 := (
0,0,0,0,0,0,0,0, -- space char
<<<row 1 of !>>>, <<<row 2 of !>>>, etc for !
<<<row 1 of ">>>, <<<row 2 of ">>>, etc for "
etc for whole of ASCII set
);


Then if you want the values for the character in signal c:
char_rom(c-character'pos(' ')) is the first row
char_rom(c-character'pos(' ')+1) is the second row

[Ahh, the days of defining user defined characters on the Beeb with VDU
commands come flooding back ]

HTH!

Martin

 

[usenet]

Thanks for the answer but I solved it on my own. Anyway, I will post it
here:

signal addr : std_logic_VECTOR(8 downto 0);

type ram_t is array (0 to 511) of std_logic_vector(7 downto 0);

-- place characters inside the ram. Each letter consists of 8 rows.

signal ram : ram_t :=

(

"00111100",

"01100110",

..

..

..

"00000000"

);

..

..

..

-- read the ram and display it to dout

dout <= ram(conv_integer(addr));





Have I nice day

Da Unseen

 

[Martin Thompson]

Thanks for the answer but I solved it on my own. Anyway, I will post it
here:

Excellent!

dout <= ram(conv_integer(addr));

This looks like some std_logic_arith... this is a very out-of-date
coding style, you should be using ieee.numeric_std these days as it's
a proper standard and better behaved than the Synopsys libraries that
they (inexplicably) compiled into the ieee lib.

See the VHDL FAQ for the detailed reasons why.

Cheers,
Martin