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Old 21st Jun 2022, 12:12 am   #2
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 834
Default Re: 6502 NOP generator

I made a universal NOP generator to test different 40 pin processors, Though I still need to add a clock divider to try it on nmos 6502s and it probably won’t work on Western digital 65C02 as I believe they have cmos input threshold voltages.

Bottom side of the board has 4 of 2x20 pin headers to connect any pin to 5v or 0v, then every pin has a 10k pull up to 5v, and a 1k to a green led down to ground, with pin headers to short any led to ground. Pins will float to between 2.5 and 3v or can be pulled down to 0.5v. Tested so far using cmos and nmos z80s, 8749 and INS8060. A 74hc04 oscillator with a socket to swap in different crystals can be connected to any pin using dupont connector cable but lowest crystal I have is about 1.8 MHz.

Idea was to use this to test a few different micros from my junkbox, but I’ve also used it to check if an 82s131 prom was unprogrammed.
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