X-Multiply EPROM equivelant

Porchy

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Hello all
Im brand new to this forum but have a little past experience with arcade pcbs.
Ive finally got round to fixing my X-Multiply pcb, the sprites have white boxes around and a few other things messed up too. Im pretty sure the mask T44.00 is on its way out, the pins are REALLY corroded. The mask is an NEC23C1000AC.
I have verrified the checksum of all the other chips and they check out fine unfortunately I cannot check this one.
Anyway, my question is what eprom will I be able to get away with for a replacement at the current rom is a 28pin and most other eproms i have seem of this size (128k x 8) are 32 pin.
Could I get away with using a 32pin 27C1001 and tieing the VCC pin (#32) to the NC pin (28).

Any help would be gratefully appreciated.
 
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Just had another thought.
The chip holders are 32 pin ones even though the roms are only 28 pin.
There is also a jumper with settings of MASK and EP, its currently set to MASK, do these stand for mask rom and eprom?
Again, thanks for any help
 
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Well, if the rom wasnt useless before, it is now. When removing it 3 of the legs stayed put and a little mod to try and read it turned up a checksum of 0000000. No choice now but to replace the rom(s).

Ive had a little look at the earlier jumper switch, can anyone tell me what these finding mean:
Reading from left to right,
the first pin goes to pin 2 on all the roms
the second pin goes to pin 22(if using a 28 pin chip)
the third pin goes to ground

I could really do with a little help on this one fellas
 

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Masked ROMs are 'programmed' by how the connections are made when the chip is fabricated... it can't be reprogrammed.

PROMs come unprogrammed (all 1's) and can be programmed once.

EPROMS come unprogrammed, but can be erased and re-programmed.

Because PROMs and EPROMs can be programmed they need extra pins for that purpose, hence a 1Mbit EPROM 27010/271000 has 32-pins, while a 1Mbit masked ROM 23010 only needs 28 (they normally go in increments of 4 pins).


To replace the 28-pin 23010 with a 32-pin 27010, you need to wire:

23010:pin 20 to 27010:pins 22 and 24 (/OE, /CE)
23010:pin 22 to 27010: Pin 2 (A16)
23010: Pin 28 to 27010:pins 30-32 (+5V).

The rest of the pins are the same.
 
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