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 Important things to know about nes eprom wiring

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Drakon
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PostSubject: Important things to know about nes eprom wiring   Thu Jan 26, 2012 11:54 am

On the nes/famicom pcbs the following rules apply when wiring up an eprom from what I've learned:

first here's a short legend:

ce: chip enable....It seems that when this pin's grounded the eprom is enabled and when you feed this pin 5v the chip is disabled and can't do anything

oe: output enable....when you ground this pin the chip is able to output data. When you feed this pin 5v the chip doesn't output.

on all nes/famicom pcbs the chr maskroms have pins for both oe and ce which is important because eproms have both an oe and a ce pin.

Sometimes the chr oe pin is labelled as "rd" but they should be the same thing. Since all chr maskroms have both a oe and ce hole on the pcb you should always wire up your eproms oe and ce pins to the correct holes on the chr spot.

prg maskroms have only a pin for ce, the prg maskrom doesn't have an oe pin. I wired up the oe pin on my rockman 1 maskrom to ground because from what I read about eproms grounding that pin enables the chip. Doing this made the chip work perfectly. I've seen guides where people wire together the oe and ce pins on a prg eprom. This probably works fine too (my earthbound zero repro cart has the prg rom wired with the ce and oe pins together).

When you burn an eprom and stick it into a spot where there's an a19 trace, you should probably wire pin 01 of the eprom to the a19 hole. Otherwise you should wire up pin 01 of the eprom to 5v.

When you burn an eprom and stick it into a spot where there's an a18 trace, you should probably wire pin 31 of the eprom to the a18 hole. Otherwise you should wire up pin 31 of the eprom to 5v.

When you burn an eprom and stick it into a spot where there's an a17 trace, you should probably wire pin 30 of the eprom to the a17 hole. Otherwise you should probably leave pin 30 of the eprom disconnected.

This is what I've figured out so far from experimentation and looking at diagrams of wiring that actually works properly.
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