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Starting a 6502 computer project, using an RPi Pico as a clock source for now 3
Starting a 6502 computer project, using an RPi Pico as a clock source for now
Starting a 6502 computer project, using an RPi Pico as a clock source for now
I just started making this a few hours ago, using parts I bought a couple years ago, before I knew too much. So far, I’ve got the 6502 running at least. The upper address lines are connected to LEDs and the data lines are just tied to the NOP instruction for now, so it just counts up, and I have a 3.5mhz oscillator (and a 3mhz crystal) that I can use, but they’re too fast to see the counting, so I used the Pico’s PIO to make a 2khz clock.
A little bit into the future, I’m probably going to add in a 6522, and some RAM and EEPROM, using a 4-16 binary decoder (though I’ve heard that I might need to gate the RAM R/W pin with the clock out signal since it doesn’t stabilize at the same time as the ram)
Also need some debouncing and power on reset, but couldn’t find anything super simple that doesn’t rely on many ICs (might use the MCU, though I would rather not)
Edit: Found what I think is a Quad NAND, I think I’ll use that to deal with address decoding and the potential issue with RAM, really old Hitachi IC though, probably from the early 80s.
A 555 makes an excellent low-frequency clock.
For debouncing at a minimum you could get away with just an RC filter, but it would make for a slow edge, so ideally you should also add a schmitt trigger inverter to clean it up.
You should chcek out Ben Eater’s channel on YT. He has excellent series on 555 clock and his breadboard computer