S.Elliott's blog

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.



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