The chaotic shambles of EPROM voltages, from 2708 through 2764

Early EPROMs required an unruly assortment of positive and negative power supplies, variously different programming voltages, an assortment of programming voltages.  And they adopted inconsistent part numbering schemes to distinguish these features.

Most surprisingly -- and irritatingly -- manufacturers gradually switched to elevated power supply voltages during programming.  So a 1977 Intel 2716 can be programmed with VCC=5 volts, whereas a 1988 AMD 2716 requires VCC=6 volts during programming.  And Texas Instruments's horribly-complicated TM2716 requires VCC=12 volts during programming!


Explore an AP-64, with and without firmware

There are a lot of AP-64 variants around, so let's explore this clone.  Nexo Distribution sold it to me as "APX-EPROM-1" in March 1988.

First, here's a close look at the firmware socket and booster circuit.


Mysterious origins of the AP-64 EPROM programmer

Last December I posted in Apple II Cards about the utterly bizarre firmware of my APX-EPROM-1 Programmer, a clone of the AP-64e that was sold to me by Nexo Distribution in the 1980s.  The APX firmware changes, depending on which slot it's installed in:



EPROM data rot in my EPROM programmer's EPROM

I recently discovered that some of my custom EPROMS from the 80's and 90's are exhibiting problems due to EPROM bit rot, which falls under the general category of data degredation...or 'data rot'.  Bit rot causes any programmed 0 bits to revert back to 1 bits, their un-programmed state.  The chip isn't actually harmed, it just loses its prorgamming. 

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