Re: Burning EPROMs

[dempson@actrix.gen.nz (David Empson)]

Herbert Fung <lemonherb1@netscape.net> wrote:

> Hi, I was wondering if there is any specific type of EPROM one would
> have to get to burn repacements for various Apple II related cards.

It depends on the card.  Older cards (or simpler ones) might use EPROMs
as small as the 24-pin 2708 (1KB).  The 24-pin 2716 (2KB) and 2732/2532
(4KB) were also commonly used on older cards.

More recent cards tended to use larger EPROMs even if they didn't need
the extra space, because the EPROMs were easier to burn and cheaper.
The 28-pin 2764 (8KB) and 27128 (16KB) were used on several cards,
including the original Apple SCSI card.  The 27256 (32KB) may have been
used on cards that needed a lot of firmware (with a significant amount
of bank switching or an onboard CPU).

It is usually possible to replace a 28-pin EPROM with one of larger
capacity, but it depends on the signals that are connected to the extra
address pins.  To be on the safe side, you should try to use a
replacement ROM of the same type as the original.  If you only have a
larger capacity ROM available, then you have the best chance of it
working by duplicating the contents of the smaller ROM into both halves
(or all quarters or eighths) of the larger ROM.

-- 
David Empson
dempson@actrix.gen.nz