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Month: August 2019

8-bit breadboard computer – eeprom programmer

Part of the output display of the 8-bit computer relies on an eeprom to drive the 7-segment displays. In order to program the eeprom, I needed to build a programmer. In Ben Eater’s youtube series, he builds a programmer with an arduino nano and a couple of shift registers because the nano doesn’t have enough digtal pins to program the parallel eeprom. I had an arduino mega with plenty of digital pins, so I used it instead.

I essentially made up a shield for the arduino with a 40 pin zif socket and soldered each pin of the socket to a digital pin on the arduino. Well, not quite every pin. That is a lot of wires. I will eventually solder every pin, but for now, I’ve got enough to cover the 28C16 eeproms.

The idea was to manipulate the pins in the sketch to fit any similar eeprom up to 40 pins. To do that, I have to define the VCC and GND pins as OUTPUT pins in the sketch and set them to HIGH and LOW respectively. Unfortunately, it seems that the eeprom draws too much current from the digital pins, so the voltage topped out at ~2 volts. I soldered on the orange wire above to the 5v rail and connected it to VCC and that seemed to fix the problem.

The code I am using is below. It is mostly modified from Ben’s code.

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