Redherring32
Sync issue when using lava RGB 1.1
Hi,
I've been troubleshooting an issue with the lava RBG board version 1.1. It seems the Lattice code depends on PPU CLK line being initialize at the right time. If using a 74HC139 to handle M2 it seem to misshandle to critical calls and send whatever eronious data to the PPU before the game the CPU is really in a ready state. I did not test did more so i'm really sorry for the lack of technical lingo here but installing a 74LS139 solve the issue right away.
Before
After
Both over composite.
Ive tested with two opentendo board with your BOM and one which i've ported from and OEM board. The OEM one did not have the issue. This is pretty much how i've spotted the issue. I don't think this is an issue with eTim's new rev 4 RGB board. It might have been in the past but since he's generating his own PPU_CLK the issue would not appear I guess.
This is from the OEM ported board buty I did test with an LS on the other board I have the issue on and the issue goes away.
U3 is our 74LS139
Also two other set of logic chips on that board should be LS version. You can't mix LS and HC. But you can mix HCT with HC and LS.
The only logic IC that should be HC is the 04.
I'll update my BOM with my findings. You can do whatever you like with this info.
Thanks
I don't think we can do anything with it on the OpenTendo side. The main purpose of OpenTendo is documentation and preservation of the NES. We want to keep OpenTendo to be as close as possible to the OEM NES. We did create a modded version which added some test points (to help with installation of other mods) and changed other footprints to modernize OpenTendo a little bit. I believe your finding is best documented with the Lava RGB.
I will leave this issue open for a while and add the informative label for users who have the same issue in the future.
I've helped a user which had the same issue with a NESRGB board from etim. The original PCB does say LS. I'd say since it does respect the preservation side and rule out any further issues like it might be a good thing to update the BOM eventually. Sometime HC and LS are interchangeable but other times one can interpret a low from a chip as a high vice-versa. But yeah at least a little note on that chip in particular wouldn't hurt.