October 2019

I purchased the MiniPro TL866II+ to write to 8k and 32k EEPROMs for the computer project. It rates pretty well and is inexpensive, so it was the only really obvious option for me.

My first attempt at writing to an EEPROM was to load a 28C64 entirely with zeros, and then load the following values starting at address $0000.

00 01 02 02 04 04 04 04 08 08 08 08 08 08 08 08
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

This is combinational logic, designed to allow a user to select a clock speed with latching buttons... only one clock is activated, based on the "fastest" clock out of the selection. The way it works is, the address changes as each button is pressed, but the value stored is based on the highest button pressed. In the case of the 4th button, there are eight possible addresses, each outputting the hex value 08. For the 5th button, there are sixteen possible addresses, each containing the hex value 10 (in decimal, that is 16).