ROM

[sirmorris]

I'm sure I've seen this covered somewhere but I can't find it - so...

Does anyone know the pin-out of the 28 pin socket that sits under my 24 pin ROM?

The board has 28-26 shorted together which makes me think this might suit a 27c64 eprom... However that thought soon disappears when I check the rest of the pinout.

It looks like I'm going to have to wire up an adapter:

socket[18] re-routed to EPROM[23] (a11)
socket[21] re-routed to EPROM[2] (a12)
socket[20] joined with EPROM[20] (/OE+/CE)

Of course I could re-arrange the data in the ROM so that I didn't need to rewire a11 & a12. But that would only reduce the re-wiring by 1 connection.

Any war stories of ROM replacement??

[Citabria]

According to my notes, pins 1, 26, 27, and 28 are all Vcc and pin 2 is A12. I once used a 2764 in the socket without adapter but, IIRC, only 4K were usable.

[Citabria]

There used to be an 8K, 24-pin EPROM completely pin-compatible with the Sinclair ROM - the MCM68764 - but I don't know if it's available anymore.

[sirmorris]

I haven't been able to find one. I think I might prefer a second option right now though; Littlejohn's posting about his 32k upgrade has made me think about putting ROM in the 8k block..

[Moggy]

Hi Citabria

try this link for the rom you are after

http://www.aeri.com/search/68764

regards Moggy