i wanted to put a 27c020 eprom on an UNROM. i was looking at this thread to get the wiring:
http://nesdev.com/bbs/viewtopi ... ight=uorom
even though it is not a 27c020 eprom being used, would this just wire up normally like an UNROM and then just add a wire from bent pin 3 of 74HC32 to bent up pin 30 of the 27c020 eprom?
You'll have to make sure you use the fourth OR gate of the 74HC32 which is not routed on regular UNROM boards. You'd want to OR the latched D3 and A14 together, and the result should be the A17 pin which is not present on UNROM.
what is the gate of the 74HC32? is that the fourth pin then? so i would wire the D3 (pin 17) to A14 (pin 29). is that correct? do i bend these pins up? thanks!
Bregalad wrote:
You'll have to make sure you use the fourth OR gate of the 74HC32 which is not routed on regular UNROM boards. You'd want to OR the latched D3 and A14 together, and the result should be the A17 pin which is not present on UNROM.
From what I looked, it seemed gate #2 was the unused one on my UNROM boards, so it's pin 4, 5 and 6. You'd want to disconnect pins 4&5 from VCC where they are originally connected, connect pin 4 (or 5) to CPU A14, connect pin 5 (or 4) to Q3 of the 74HC161 (pin 11) and connect pin 6 to A17 of the PRGROM.
Also, D3 of the 74HC161 (pin 6) have to be un-connected from VCC where it is originally connected to, and to be connected to CPU D3.
After all that you should have turned your UNROM baord into a fully functionnal UOROM board (if you also do the normal modification for the EPROM pinout).
I can't be absolutely about pin numbers because some other revisions of UNROM may have assigned it differently (the OR gates could be reasigned in any order, so could the 4 latches in the 74HC161), but there is a good chance that what I told applies to all Nintendo made UNROM boards.
cool, ill give this a shot then and let you know how it goes