Back in January there was a discussion going on over on the Jamma+ forums regarding the D77-14 and D77-15 PAL dumps.
After a lot of help from various people and testing by myself here is the conclusion I have come to regarding this issue.
D77-14 is used when the main CPU ROM’s are 27c2001 (0x40000).
D77-15 is used when the main CPU ROM’s are 27c4001 (0x80000).
On a 27c2001 EPROM, pin 31 is the programming pin. It is active low so once the chip is programmed we want to keep this held high when in use. That’s exactly what the D77-14 PAL is doing. Pin 19 of this PAL is fixed HIGH and is connected to pin 31 of the 27c2001 EPROM.
On a 27c4001 EPROM, pin 31 not the programming pin but it is the upper most address bit and that’s why with a D77-15 pin 19 is able to toggle which allows for double sized EPROM’s to be used.
This is where the confusion comes in.
On many converted boards out there in the wild (and there is a lot of them) we have found there to be D77-14 stamped PAL chips with the same code as what we have found in D77-15 PAL chips and vice versa. Assuming the PAL chips themselves are the original ones from Taito (and I have no reason to see why they wouldn’t be) then my theory is, as they are all PALCE16V8 chips, which are reprogrammable, they have simply been reprogrammed by the bootlegger/converter to use whatever version they needed. This would keep it looking that little bit more authentic and also cuts down on the cost of buying a GAL16V8.
If you check in the MAME source too, every game that has program ROM’s of size 0x40000 uses the D77-14 PAL and every game that has program ROM’s of size 0x80000 uses a D77-15 PAL.
Hopefully that will clear up a bit of the confusion surrounding this.
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