A great read, both as a more in-depth intro to Acorn MOS and some details about Ruby.

Hjalfi, if you need an advanced 6502 assembler you might want to have a good look at Jasm. Open source, fast and very good to use in my opinion. I'm having trouble NOT using it in my old projects.
http://kollektivet.nu/jasm/

Very nice, congrats!
Will have a good look at it.

I use cupl in Linux/wine without any problems. The WinCupl program never worked OK at all for me, regardless of OS, but the DOS executable is good.

Thanks for your sharp eyes BDD! I've mixed and matched way too many sources to be sure what way is up
Updated doc with:
- BRA -> BRK
- BBR, BBS, RMB and SMB uses official syntax
- INA, DEA -> INC A, DEC A
New version 0.2.1 available in first post.

I've updated the doc:
- Use SP for Stack Pointer, SR for Status Register.
- Changed the wording on BIT.
- Changed to a compact text-document, 78 chars wide.

A text document was what I really wanted in the end, but it was so much simpler to edit text in a spreadsheet. If anyone wants a pdf or the ...

BDD: you are correct. I'll have to think about how to phrase it better.

A test showed that it is indeed correct that BIT immediate only changes the Z-flag. Updated doc added to first post.
I'll have a look at that book, I only read summary documents which was what I needed. Will be interesting to see how the book matches my findings

Thanks for the report, I'll make sure to test it on my setup and update the doc. I've read 3 different versions of WDCs docs and 5-6 other, and they all seem to think that BIT imm DOES transfer bit 6 and 7.
Trying to get proper docs for the 65C02 has been such a frustrating exercise, the only upside ...

I've looked at several 65C02 documents, but they all seem to disagree on the instruction timings. Today I got bored and wrote code and counted cycles. Attached is a document formatted to my preferences with my findings.
This was run on real HW, a Teensy 4.1 simulating memory and controlling a brand ...

This looks very good, hoping to get some time in the not-so-distant future to test it out!

Cjs: I agree with you, I've just had too much fun by myself instead of sharing. I'll retrace what code is used from where and give proper credit.

Floobydust: I have not gotten the ATF750 programming working with your suggestion. I'll try again later, but for now I'll use the Teensy to do all the ...

Hello, new to this forum but not new to 80s tech and computers. I've read the forum for years but became a member only yesterday. So much good info and many great discussions!

My first computer was a ZX81. Still my favourite retro platform, even if Z80 is not my preferred assembly version.
Lots of ...

A great implementation, very interesting to see the source!
I was scratching my head for a while on how you managed without level converters on the address bus, but of course they are outputs. Only inputs will fry on 5V from the system :) Might be nice to explain somewhere in the manual for future ...