DVI/HDMI with increased blanking?

TonyB_

I don't have the Eval digital video board hence this question. Is it possible to use 300MHz sysclk to display 640x480 by increasing horizontal blanking and total from 160 and 800 to 312 or 313 and 952 or 953, respectively? Vtotal unchanged at 525 lines.

rogloh

It should be, though it's probably monitor dependent. As I have something all ready setup to test I'll give it a try with my new Bull Ant board and Dell 2405FPW shortly and report back very soon...

Wuerfel_21

Yep, should work. The HDMI modes in my emulator programs work like that, though they signal 800x480 and still have to generate large Hblanks. For that application it is important that the vertical blanking is not increased.

TonyB_

@rogloh said:
It should be, though it's probably monitor dependent. As I have something all ready setup to test I'll give it a try with my new Bull Ant board and Dell 2405FPW shortly and report back very soon...

Thanks, Roger. Aim is to have a nice round 300MHz sysclk instead of 252MHz. Htotal of 952 is a multiple of eight and might be better value to try (first post edited accordingly).

rogloh

Yep worked with my driver and I have a stable picture. Monitor reports 640x480 60Hz.

I used these settings with 73 extra in the front porch and 80 extra in the back porch to make up the full 313 blanking.

vga_timing         'VGA resolution 640x480 60Hz with 300MHz P2 clock
            long   0 ' was originally CLK252MHz
            long   300000000 ' was originally 252MHz

                   '_HSyncPolarity___FrontPorch__SyncWidth___BackPorch__Columns
                   '     1 bit         7 bits      8 bits      8 bits    8 bits
            long   (SYNC_NEG<<31) | ( 89<<24) | ( 96<<16) | (128<<8 ) | (640/8)

                   '_VSyncPolarity___FrontPorch__SyncWidth___BackPorch__Visible
                   '     1 bit         8 bits      3 bits      9 bits   11 bits
            long   (SYNC_NEG<<31) | ( 10<<23) | (  2<<20) | ( 33<<11) | 480
            long   10 << 8 ' $0ccccccc+1
            long   0
            long   0   ' reserved for CFRQ parameter

rogloh

The other 952 value was also tested and works too (front porch reduced by 1 to 88 from above).

TonyB_

@rogloh said:
The other 952 value was also tested and works too (front porch reduced by 1 to 88 from above).

Great, many thanks.

evanh

Generally, for LCDs, DVI timings are a lot lot lot more flexible than VGA timings for the same LCD.