Post by Jorge Post by Michael J. Mahon Post by Jorge
This card gives 21 volts at VPP pin 21, this EPROM I want to program says
12.75. Will I fry it with 21?
You'll need either higher programming voltage EPROMs or a card modification
to provide the lower programming voltage.
I have injected 12.8v throught the on/off switch, looking at the schematics
(appleii-box.de) that's the best way to do it. Unfortunately it does not
work 100%, some bits in some bytes can't be flipped to zero, or perhaps
that eprom is kaput, idk.
EPROMS have standard protocols for programming, and many newer programmers
take that as a starting point and improvise. ;-)
For example, the software may try n shots at programming, reading after
each try, until it sees the correct state. Then it may do another n cycles
just to be sure the bit is well and truly programmed (or maybe 5n).
This has the advantage of adapting to the characteristics of the EPROM
I doubt that any Apple programmers did that, but it's high time that better
firmware was written--to an EPROM, of course! ;-)
-michael - NadaNet 3.1 and AppleCrate II: http://michaeljmahon.com