Re: Burning EPROMs

["Stephen Shaw" <bottrawler@junkbuster.zzn.com>]

On Sun, 15 Dec 2002 16:13:45 +1300, David Empson wrote:

> 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.

2708s are obsolete and most EPROM programmers that can handle the 2716s
upwards do not seem to handle the 2708 (different programming voltage?).
I have a lot of Epson APL printer cards minus their 2708s :(



> 
> 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.