Unfortunately sim65 doesn't really have any debugging features.
What are you looking for exactly? I wrote a full 65C02 implementation in Swift ( https://github.com/nrivard/Microprocessed ) that is fully covered by unit tests so you can see how it works. If you are comfortable with Swift, you could ...

You really need to separate the Ø2 clock from the X1 clock.
Everyone has to make trade-offs. For me, the trade-off was (and still is) everything must fit on a 100mm x 100mm board. Ultimate speed is not my real aim, I was actually pretty happy with 2Mhz on v1 of the board, so 7,3728 would be more ...

It turns out the interrupts weren't firing because I was writing to $05 (the IMR offset) instead of DUART_BASE+$05 :( All cleared up now. So far no problems running both the system and 28L92 from same 3,6Mhz main clock source.

I also pushed actual GAL PLD code which does not qualify CLK with any CS ...

This was very helpful, thank you. Armed with this, I now have everything working synchronously (basically just replacing my old synchronous get/send byte routines). The only issue I've found so far is probably from either my terminal software on the connected computer or the CH340 usb-to-serial chip ...

Ok I have to write values to MRx as well. Haven't nailed down exactly which ones, i just wrote zeroes to all 3. Then wrote baud rate. then did the code originally posted and it works. I was going to write MRx values anyway but now I know.

Ok weirdness ensues. Can't get it to work again even following exact same steps, but timer/counter and IRQs are working now at least. More debugging! One big positive is that I was able to take my VIA expansion board out. I was using VIA timer to generate system clock and now it's fully onboard ...

There are series resistors

The reference to a delay of up to two bit times strongly suggests that the baud rate divisor must be set up before you can use the functionality.
This did it! Just had to actually write a value to the baud select. Thank you! I'm happy to see i didn't completely screw up wiring. Now to get the ...

I am trying to bring up my SC28L92 on my new SBC (see this post for hardware spec) and so to start, I just want some blinky lights. My hardware has LEDs connected from +5V to TxD and RxD lines so I thought if I can set Tx via the 28L92, I should be able to see some lights!

However, these efforts ...

- It would have been more flexible to have separate the clocks for the CPU and the SC28L92.

Yes it would, but one of my major goals was to just make it as compact as possible to get that sweet JCB PCB price point, $8 for 5 4-layer boards as of this writing. In the future, if things go well, I ...

As promised here are some real-world photos of the n8 Bit Special in action! My first test was a free-run test. I hardcoded $EA on the databus and observed the low 6 address bits from an expansion port. A very complicated clock divider!
n8bit_v2.jpg
Next I hooked up RAM (x2), ROM, a VIA and an ...

At long last I have received PCBs for the 2nd iteration of my SBC: the n8 Bit Special. The n8 Bit Special is an open-source 65C02 SBC with core functionality on a 100x100mm 4-layer PCB and 3 ports for small and focused expansion cards. Hardware information, PCBs, GAL code, etc. can be found here on ...

I have found it essentially impossible to get FTDI devices now due to the global chip shortages. My design called for the FT230XS but at one point ship times for those were October...2023! I sometimes see small quantities pop up but because of the shortages I have since switched to the cheaper (and ...

Happy to contribute back I am hoping to have an interesting simulator for macOS and iPadOS sometime in the near-ish future built on this core so stay tuned.

I've written and recently open-sourced a full 65C02 simulator core written entirely in Swift. It passes the Klaus functional tests, extended opcode tests, and the Bruce Clark decimal tests. If you want to contribute or are just curious, you can find the project on github:
https://github.com/nrivard ...