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Re: Premier's Sprite Graphics Board
Posted: Sat Jul 27, 2019 2:16 am
by Pernod70
dublevay wrote: ↑Sat Jul 27, 2019 12:50 am
My question is does the EXEC &HE002 directly execute the same &HE002 as I can PEEK from BASIC (which is just full of 0x7E), or does some strange decoding happen which makes the EXEC command somehow get routed to the &HC000 location?
The ROM is mirrored, so you should see the ROM at &C000 and &E000.
Re: Premier's Sprite Graphics Board
Posted: Sat Jul 27, 2019 8:55 am
by dublevay
Definitely not seeing that. Any idea how the mirroring is done?
Re: Premier's Sprite Graphics Board
Posted: Mon Jul 29, 2019 11:24 pm
by dublevay
Made some progress on this tonight. It seems that by replicating a patch on the prototype board by breaking the link between L & M, and then connecting L to D, the ROM mirrors between &HC000 and &HE000. However, replicating the EPROM mod doesn't seem to work correctly. On the proto board, X & Y are connected, whereas on the green board, Y & Z are hard linked. X is actually A12 from the cartridge port, whilst Z is ground, and Y is A12 from the EPROM. However, connecting X & Y results in the EPROM code disappearing from &HE002!!
I have some new ICs coming tomorrow. Although I can test a lot of them using the MiniPro, some cannot be tested, like the 7425 or the 4066 - so I figured some new ones would be better.
Re: Premier's Sprite Graphics Board
Posted: Tue Jul 30, 2019 6:29 pm
by dublevay
It's teasing now. Not sure if my new components have fixed it, but I have discovered that the 12V supply has to be pretty accurately between 11.9v and 12v.
Still need to work out how it's supposed to be reading the top half of that EPROM!