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GPIO Test on a C64: PASS

Posted on July 10, 2012 in Category: Blog - 0 Comments

GPIO Testing on a Commodore 64

Today I tested the General-purpose I/O which the AVR uses to talk to the C64 on the user port. In this test, I wrote a quick BASIC program that changes the state of the user port lines, counting from 0 to 255 and outputting that value on the user port. Then I had a program running on the AVR that monitored the GPIO state and output it to a serial line which I monitored on my PC.

The test passed, but had one strange anomaly. Every time I changed bit 4 from low to high, there would be this long delay. Not sure what that's about, but I'll get it figured out. It might be a bad solder connection or perhaps one of my traces.

This design is not yet final because I am likely moving to another chip which won't require this feature. However, I may still include it in the next design as a user-programmable I/O. All the other peripherals on board will likely be connected without the need for the GPIO.

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