I have an SLG 3000 v2 scanline generator. It works great at 640x480 60Hz in Windows on my old Pentium computer. However, I can't get the scanlines to appear correctly in MS-DOS with 720x400 at 70Hz, or even 640x480 at 60Hz when I change resolutions. They appear but flicker, like an interlaced picture. My monitor shows the signal is 31kHz horizontal and 60Hz vertical. So not sure why 640x480 60Hz works in Windows but not MS-DOS, the signals should be the same.
Perplexed, I did some reading in this really old thread. Seems to be the original SLG 3000 announcement thread. It has the ability to power itself from the sync signals without an external 5v power source. I'm wondering now if I need 5v power for this thing to work correctly. My understanding is the reset pin on the flip-flop chip is wired in to vertical sync. Perhaps if that vertical sync signal gets too low because the board is using sync for power, it won't trigger the reset and will cause the flicker. I may be wrong.
viewtopic.php?f=6&t=33454
Does anyone have experience using the SLG 3000?
Edit: Looks like I'm right on the money:
viewtopic.php?p=917639#p917639
He is referring to this post with the same flickering as his and mine:
viewtopic.php?p=688019#p688019
Also noticed this post:
viewtopic.php?p=654715#p654715
This confirms it uses horizontal sync, not vertical sync. Because horizontal sync uses a positive pulse. It's possible then, with this particular computer, the amplitude of the horizontal sync pulse is lower when the Windows driver isn't loaded. It's probably enough to drive the flip-flop chip and advance the clock pin, but not enough to reset the chip on every vertical refresh.
SLG 3000 V2 Flickering Scanlines (SOLVED)
SLG 3000 V2 Flickering Scanlines (SOLVED)
Last edited by titan91 on Wed Dec 25, 2024 5:18 pm, edited 1 time in total.
Re: SLG 3000 V2 Flickering Scanlines
Unfortunately adding a 5v supply did nothing other than brightening the power LED slightly. When the Windows driver is loaded the card appears to output TTL level vsync and averages to 3.66v according to my multimeter. When in DOS, its output appears to switch to line level vsync and averages to 0.38v. I don't have an oscilloscope to verify the exact peak-to-peak signal levels, but TTL sync should be 5v.
Is there an interrupt or register that can be changed in MS-DOS mode to switch vsync to TTL level, maybe via a TSR?
https://imgur.com/a/q3wIPRS
Is there an interrupt or register that can be changed in MS-DOS mode to switch vsync to TTL level, maybe via a TSR?
https://imgur.com/a/q3wIPRS
Re: SLG 3000 V2 Flickering Scanlines
Thank you both for the input. For anyone wanting to get the intended scanline look themselves, I was finally able to figure this out. I used the LCD640 TSR from this thread to invert the vertical sync polarity.
https://www.vogons.org/viewtopic.php?t=86219
https://imgur.com/a/4IlCSdz
With vsync now set to negative, the same as in Windows, the SLG3000 v2 scanline generator now works properly in 320x200 VGA mode DOS games. The results are great! I just created a BAT file and called LCD640.COM before starting the game. It also uninstalls the TSR when I quit the game.
https://imgur.com/a/8720TyS
https://www.vogons.org/viewtopic.php?t=86219
https://imgur.com/a/4IlCSdz
With vsync now set to negative, the same as in Windows, the SLG3000 v2 scanline generator now works properly in 320x200 VGA mode DOS games. The results are great! I just created a BAT file and called LCD640.COM before starting the game. It also uninstalls the TSR when I quit the game.
https://imgur.com/a/8720TyS