Dr Jefyll wrote:
Yes, this is certainly important. It's not a good sign that you were "measur[ing] high frequency oscillations between 0 and 5v on all the data lines and address lines."
"
" Indeed... I don't think that was caused by noise, maybe my ground probe was detached or something, although I find that unlikely.
I should note that this breadboard version and the schematic I posted of it isn't really similar to what I have soldered, it was just a test to see whether my ic's were broken or not and whether I was still able to create a minimal working system.
The clock on the soldered version comes from a 1mhz can oscillator, so I assume that should provide a clean clock signal. It has worked before anyways. I also made a simple reset circuit that not only should provide a clean reset signal, it also provides two reset signals, so you can make sure that the IO resets before the 6502.
BigEd wrote:
So, clock and power are well worth getting very clean
Dr Jefyll wrote:
I'm more suspicious about bypass caps and power, and the clock signal
I did take care during soldering of ensuring good power and ground connections, as well as 100nf bypass capacitors, so I think that shouldn't be a problem. The power supply is a simple 2n3055 emitter follower to step down 12v to stable 5v, along with a 1000uf electrolytic capacitor. I'll try however whether I can measure any significant noise.
Dr Jefyll wrote:
On older 65xx systems it was SOP to take the Phi2 and /Phi2 signals from the outputs on pin 39 and pin 3 of the 6502
I believe I did once try to get the phi2 for the 6522 from the phi2 output of the 6502, but that didn't work, so I then decided to just use it directly from my clock.
Since I got a computer up and running before soldering one, I can rule out most possiblities. That means that the problem should be a soldering error or something that I have changed. I triple checked every connection and possible shorts, so I don't think there is a soldering error. The only things I changed were the memory map, the reset circuit and the power supply. I have confirmed the reset circuit works. The power supply also works, but it may be noisy, so I will try powering the computer from my bench power supply. At first I also did make a dumb mistake in the memory map, as I reserved 48K of RAM for a 32K chip
. If it can be of use, I'll draw up a schematic of the memory map.