Felix

VGA Question

8 posts in this topic

I know nothing about VGA, but had a question..

On the Arcade and LogicStart boards,

why are there only 2 resistors on the blue while there are 3 on the red and green?

Edited by Felix

Share this post


Link to post
Share on other sites

Hi,

not sure but take a look at the source code

vga_r <= vga_ram_data(7 downto 5);

vga_g <= vga_ram_data(4 downto 2);

vga_b <= vga_ram_data(1 downto 0);

Maybe the Logicstart was tailored for the VGA driver.

BTW the Arcade Megawing has 12b colours (4 resitors for each colour)

1 person likes this

Share this post


Link to post
Share on other sites

thanks :)

i wonder if thats why my flatscreen tv doesnt like the papilio arcade.

however, for the hardware thats being emulated it should be plenty, i guess.

Share this post


Link to post
Share on other sites

I would check the frequencies, I would guess some tv's are a bit picky on those?

I haven't tried mine on the tv yet, will be interresting to try.

Share this post


Link to post
Share on other sites

You are probably right...

iirc, most of the original arcade boards used 15Khz/60Hz...

from the manual :

Supported Display Resolution

•Computer formats

Resolution @ Refresh rate

---------------------------------------

640 x 480 @ 60Hz

800 x 600 @ 60Hz

1024 x 768 @ 60Hz

1280 x 1024 @ 60Hz

1360 x 768 @ 60Hz

1600 x 1200 @ 60Hz

1920 x 1080 @ 60Hz

I wonder if this is something that can be adjusted in the vhdl ?scan doubler? file

sadly, @ work atm so can't even peek there. of course, who knows what else that would break.

Share this post


Link to post
Share on other sites

As to why 2 bits for blue, but 3 for green and red... The eyes are more sensitive to red and green than blue, so an doubling the number of red and green levels vs blue gives best results.

I've had Pacman running on a older 40" Sony V series, So it can't be that far off... Maybe run iSim and check the hSync frequency.

Share this post


Link to post
Share on other sites

that makes total sense.

i decided that i am not going to worry bout running the arcade stuff on the big tv since its all sideways anyways, and the wife would kill me if i turned the flatscreen on its side :)

i will try with the A2601 stuff see if that shows up tho.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now