6502.org

The GAL circuit should have worked fine, since the GAL's output actively drives in both directions. What I don't see in your reset circuit is a pullup resistor on the DS1813's output. The DS1813's internal pullup is too weak and relying solely on it will make the circuit noise-prone, something I determined via testing on the original POC V1.0 unit I built in 2009. You have the same potential problem wired into your new reset circuit. I suggest you add a 3.3K pullup to the DS1813's output.

There were a lot of great suggestions for improvements, and I will definitely keep them in mind for a future revision of my PCB, but I decided to go ahead and order some PCBs based on my original design and layout.
My eyesight isn't what it used to be, and I haven't admitted to myself yet that I need bifocals or reading glasses, so soldering wasn't as fun as I remember it being. But, besides occasionally needing to use a magnifying glass, I didn't run into any issues.
After soldering, I double-checked that there wasn't a dead-short between +5v and ground, then connected power and double-checked +5V at the various sockets.
After installing the components in the sockets and powering up, everything appears to be working correctly. I have not tested all of the I/O but I have not encountered any problems so far.
Thanks again to everyone who suggested improvements!

Shawn

Here it is running Floobydust's C02 BIOS, monitor and EhBASIC.
My next steps will be to write my own BIOS and monitor. After that, I plan to get Forth running.

Shawn

Excellent! Well done.

Oops! I went out of order.
Here it is running Tali Forth 2.

Shawn

Good job. The first revision of my PC board is nearly ready to go. Just need to decide on a UART. I have written some bit banging code for the 65C22, but for sanity I think I'll either put a 65C61 or the NXP UART on the board. How did you find the NXP to program?

How did you do your decoupling capacitors on in EDA? I am using Kicad and its a bit of a mess adding capacitors directly to the power rails on each IC.

Not bad. It is a little more complicated to initialize than a 6551, but it is much more capable and doesn't have the 65C51 TX bug. After initialization, transmitting and receiving data is very straightforward.
BDD has written some documents that explain really well how to use the NXP UARTS. You can find them in this thread - UARTs: REPLACING THE 65C51
I use KiCad too. It seems to be common to put all of the bypass capacitors together on your schematic like this. Then you can position them close to the ICs on your PCB layout. Shawn

I've written a BIOS for the 65C51 and the NXP SCC2691. While the NXP is a bit more involved, I would strongly recommend using the NXP UART. You also have the 16-bit timer which can be used as a Jiffy-Clock and will be consistent regardless of the processor clock speed. With the 28L92 DUART, you have the second serial port should you need it and some I/O lines as well.

You can take a look at my BIOS code (github page) to get an idea on the BIOS for both the 65C51 and the NXP. Note: Don't forget that the current W65C51 has the xmit bug, forcing you to write code around it. Good luck!

Indeed, one way to look at it is that the 28L92 replaces two 6551s and half a 6522, all in one convenient package.

That is a good idea regarding the capacitors. I'll give it a try.

I have some PLC44 DIP adapters so I'll order the NXP UART and give it a go.

Thanks.

I just spent 45 minutes watching drogon make hot cross buns and soda bread. Now I'm hungry!
It's nice to be able to put a face with a user and see them doing something else they enjoy.

Shawn

Ah. The bakery... I had to close that down start of last lockdown in the UK, so not done much backing since... It was a hobby that got out of hand!

Here's something else I enjoy

https://www.youtube.com/watch?v=zi4m9eRZq9g

Cheers,

-Gordon

Me watching video
...
"There's a tunnel!"
...
"And a bridge!"
...
"And another bridge!"

So cool! Thanks for sharing! After reading the description I watched again to see the ABS in action.
I also watched your POC V1 Demonstration video. I would have watched it sooner had I known about your YouTube channel.
I had planned to work on my BIOS and monitor, but now I've spent an hour watching 1.6" scale train videos on YouTube! No regrets!

Shawn