Hackaday.io page with schematics and more details: hackaday.io/project/192630-fast-pdip-6502-computer 6502.org forum thread with design discussion: forum.6502.org/viewtopic.php?f=4&t=7670
Great explanation George! I'm impressed with how fast you got the breadboard version going and surprised you did have more decoupling evident. I ended up making some custom sockets with decoupling caps to make some chips table at 25mhz.
Thanks James, yes I saw those, it's a nice idea, keeping things neat and reusable. I've never really managed to do good decoupling on breadboards, and mostly came to the conclusion that you just need to tolerate a lot of noise, for this and other reasons - it's not an ideal environment! The PCB version has good decoupling though, and a lot of care taken with trace routing and ground returns, on two-layer boards. I built a good ground network on the breadboard too, so all signals should have an OK route for the return current, and added some decoupling at the power rails after finding that one specific test case was failing - the TSB instruction with quite specific inputs - apparently due to a dip in power input to the RAM!
Haha thanks, glad you approve - again metastability is not my speciality, but I applied what I thought was best practice. Long term I will probably redesign it with the I/O clock divided down from the CPU clock, so that issue will do away, but I'm glad I did it this way first.
Very cool. It makes me want to break out the wire wrapping tools again. Your project takes me back to the mid seventies (but MUCH slower; only 1MHz). I'm looking forward to your demos.
I appreciate being able to follow along - excited to see what you do with it 😊 One of the projects in my backlog is quite the opposite direction: A no-ROM toggle switch computer - NMOS compatible of course. I’m thinking Woz’ RDY single stepping and some 245’s should do.
Great Video and thanks for explaining how the clock stretching works, a simple yet very effective technique! It’s a sixty five oh two for me too (as I’m on the same side of the pond as you)!
Yes, my initial design did use RDY - the inverse of IOWAIT is exactly that signal, it just fed through a resistor to RDY. It worked OK, but I changed it to clock stretching because I was unhappy with the slew rate of RDY through the resistor.
Haha, I'm afraid I learned to say it this way 40 years ago when there wasn't much opportunity to hear other people saying it. So I thought of it this way in my head from the beginning. Besides, how could you go against the 6502 song? ruclips.net/video/LrPxM-qYNTI/видео.htmlsi=tHlEjEmQWWRj2Ay3&t=36
We always said six-five-oh-two in the UK back in the day... it's taken me years to get used to people saying sixty-five-oh-two. We always said Zed-eighty too.
Interestingly it looks like Chuck Peddle said "sixty five", as well as "sixty eight", "eighty eighty", etc. I've always read the digits out one by one for all such codes, I think, even more common ones like "eight oh three eight six" etc
Hackaday.io page with schematics and more details: hackaday.io/project/192630-fast-pdip-6502-computer
6502.org forum thread with design discussion: forum.6502.org/viewtopic.php?f=4&t=7670
The clock stretching circuit is clever, and simpler than I expected.
Thank you for explaining clock stretching in a way even I can understand!
Great explanation George! I'm impressed with how fast you got the breadboard version going and surprised you did have more decoupling evident. I ended up making some custom sockets with decoupling caps to make some chips table at 25mhz.
Thanks James, yes I saw those, it's a nice idea, keeping things neat and reusable. I've never really managed to do good decoupling on breadboards, and mostly came to the conclusion that you just need to tolerate a lot of noise, for this and other reasons - it's not an ideal environment! The PCB version has good decoupling though, and a lot of care taken with trace routing and ground returns, on two-layer boards.
I built a good ground network on the breadboard too, so all signals should have an OK route for the return current, and added some decoupling at the power rails after finding that one specific test case was failing - the TSB instruction with quite specific inputs - apparently due to a dip in power input to the RAM!
So many ignore metastability issues, KUDOS to YOU! :) btw, neat design, love it! :)
Haha thanks, glad you approve - again metastability is not my speciality, but I applied what I thought was best practice. Long term I will probably redesign it with the I/O clock divided down from the CPU clock, so that issue will do away, but I'm glad I did it this way first.
Very cool. It makes me want to break out the wire wrapping tools again. Your project takes me back to the mid seventies (but MUCH slower; only 1MHz). I'm looking forward to your demos.
Thanks David, I'll have to write them though! So far I've mostly been running test suites.
Those were good days when 450ns RAM came out then we could just barely get our 6502s running at 2 MHz if we could keep everything cool enough.
Love it! Big fan of continuing to build homebrew projects with PDIP (easier on older eyes and fingers than SMD).
I appreciate being able to follow along - excited to see what you do with it 😊 One of the projects in my backlog is quite the opposite direction: A no-ROM toggle switch computer - NMOS compatible of course. I’m thinking Woz’ RDY single stepping and some 245’s should do.
Nice Job! At times I think I have more fun designing the hardware than I do programming it.
Great Video and thanks for explaining how the clock stretching works, a simple yet very effective technique! It’s a sixty five oh two for me too (as I’m on the same side of the pond as you)!
Whoops… I meant to say Six five oh two!
Did you look into using the RDY pin? I started work on a DMA system that would use it but a better idea came to me so I never followed through.
Yes, my initial design did use RDY - the inverse of IOWAIT is exactly that signal, it just fed through a resistor to RDY. It worked OK, but I changed it to clock stretching because I was unhappy with the slew rate of RDY through the resistor.
thank you for this i look forward too more of your videos
Brilliant mate!👍
Great video George :)
Thanks Gary!
Very nice.
Please call it a "sixty-five ooh too!" instead of anything else. My brain can't cope otherwise.
Haha, I'm afraid I learned to say it this way 40 years ago when there wasn't much opportunity to hear other people saying it. So I thought of it this way in my head from the beginning. Besides, how could you go against the 6502 song? ruclips.net/video/LrPxM-qYNTI/видео.htmlsi=tHlEjEmQWWRj2Ay3&t=36
We always said six-five-oh-two in the UK back in the day... it's taken me years to get used to people saying sixty-five-oh-two. We always said Zed-eighty too.
Interestingly it looks like Chuck Peddle said "sixty five", as well as "sixty eight", "eighty eighty", etc. I've always read the digits out one by one for all such codes, I think, even more common ones like "eight oh three eight six" etc