I know it's kind of pontless, but I want to make my own PC Engine 6 button pad circuit, before I start I wanted to check if anyone has done this before, could save me the trouble.
There's really nothing to it, it uses three of the same chips the regular controller has only one of. I've at one time made up a diagram showing how it works, but I seem to have lost it, it's not where it should be (http://www.gamesx.com/controldata/turbocont.htm). The relevant data is there tho, with that page and a screwdriver you should be able to map out the guts of the pad in about 20 minutes.
I should have been more specific, the only thing that puzzles me is the 3 select and 3 enable pins, how they are handled with a 6 button pad.
The way I understand it, one 74hc157 takes the outputs of the first two 74hc157 ICs, one has the standard inputs, up/down/left/right/I/II/start while the other takes G/G/G/G/III/IV/V/VI (not particularly in that order).
So I'm guessing something else has to be done, otherwise the 74hc157 would end up taking the same outputs from the first two....
I hope I am making sense, this would be so much easier with a real 6 button pad, all I have is a third party pad that uses custom ICs, with the markings sanded off.
Yeah, you've got the situation right. Where a normal pad has a '157 that switches UDLR and St/Sl/I/II (a two-stage process) the 6-button has a four stage process, using one '157 to switch between the other two. If I had the diagram I'd give it to you. Might have it in an old book, in fact...