The Eprom Programmer is connected to a parallel port. It is intended to program 2764, 27128 and 27256 eproms with a 12.5V vpp.

The 12.50 programming voltage is generated using a TL497. The 6V vcc programming voltage is generated from the programming voltage using a 7806 regulator. The programming and vcc programming voltage are switched to the normal 5V vcc voltage using a relais.

The programming data and addresses are written on the parallel port (D0..D7) and latched using 3x74LS374 and a 74LS273 (for control). The STROBE, AUTOFEED, INIT and SELECTIN parallel port outputs are used to control the latches.

The programming slot (28-pins) is read using a 74LS151 which sends one bit (the selected bit being read) to the parallel port ACK input. While reading, the data programming latch (74LS373) is in tri-state.

(click on the picture to enlarge)