Rare type of single-output flip-flop may have Q instead of !Q
msinger opened this issue · 0 comments
There is a rare type of flip-flop that has only one output. It is used on pages 12 and 32 only.
On page 12 (CH1 Sweep) there are two columns with these flip-flops: DOLY
...GALO
and DEVA
...HORA
.
On page 32 these are all the flip-flops that have a !RESET input but no !SET input, like RAWU
.
The schematics show those flip-flops with a connected !Q output and an unused Q output. However, for APU channel 1 to work, this must be the other way around: Q output used, !Q unused (or better not drawn at all). When CH1 gets restarted, it first resets all of those flip-flops. Their outputs are connected to some full-adders. The carry output of the full-adder of the highest bit acts as a stop trigger for CH1 (it goes through CORU
->BYLE
->ATYS
->BONE
->BERY
and then into the RESET input of CYTO
(see #29)). So if those flip-flops had !Q outputs, then they immediately cause all carry outputs of those adders to be 1, including CORU
, which causes CH1 to stop before it even has started.
This is why I think that they must have Q outputs instead. I'm not 100% sure, because I haven't simulated the PPU yet.
@rgalland, in #53 I asked about MEGU
before, which was a different type (it doesn't have !RESET), so I'm not sure now if you meant all single-output flip-flops on that page when you said, that they have Q outputs?