Ben Eater 6502 Kit — Day 9

in Project HOPE2 months ago


Good news. The CPU wasn't damaged after all. The RES (Reset) pin was bent inwards. To bad I didn't make a photo to show how that looked like.

Anyway, with the RES not connected to either ground or +5V the CPU would act entirely random and unpredictable. It would even change behaviour it I brought a finger close to RES pin. Which was very weird.

With the RES pin connected the CPU started to act predictable. Only the address bus was still acting strange. Looking closer I noted that I have all the Arduino lines connected the wrong way around. After I fixed that the reset sequence went trough just as shown in the video.

Screenshot at Nov 09 175424.png
Monitor output of the reset sequence

The next thing to do is replace the 1kΩ resistors encoding hex EA on the data bus with an actual ROM so we can execute some real programs.

6502 NOP operation hard coded with 1kΩ resistors

I'm also tempted to add an simple disassembler to the monitor program to get some easier to understand output.