A mistake occasionally seen with this sort of thing is using the Ø2 clock to qualify the 65C22’s chip select and read/write inputs. That is incorrect design and depending on signal skew, the phase of the moon and the state of the stock market, may result in intermittent or no operation.

I can't ...

I have spent some time over the weekend reading through the primer and it is truly an excellent resource. I can see the issue with the RAM timing and I will adjust my circuit accordingly. I'll try breadboarding it out with all the changes I've made. I'm having a lot of fun with this!

Thanks for the feedback folks. I have taken some of the advice on board and added a proper clock generator. I also added 8kB of RAM, which I had on hand.

6502PrototypeRev2.PNG

I have since bought some 32kB RAM chips which I will play with next.

In the meantime, I turned my original design into ...

Thanks a lot for the feedback. I didn't even realise the SOB pin was an input - how did that get by me? I will be sure to tie it to Vcc.

I couldn't think of another way to get such a slow clock rate apart from using a 555. It seems to be working, but I'm definitely open to other options - any ...

Hi all, newbie here. Thought I might share this project I've been working on.

Many years ago I studied Electronic Engineering in college, but then I got a job as a software developer and never touched electronics again. It's been nearly 20 years, but lately I decided I wanted to fiddle with ...