6522 Data sheet with searchable text, not in diagrams

[tricky]

I am revamping my 30 year old BBC Micro emulator and decided the 6522 was a mess.
The whole emulator was written and tested using chuckie egg, so wasn't the best and I think it was from a ROM version, I can't remember but never added tape or disc so it will have been loaded directly into RAM if not.

There is a google docs version that is viewable and presumably copyable here: https://docs.google.com/document/d/1hft ... drive_link
I don't know if it needs a login as I don't use Google Docs much.
You don't need a login to view the Google Doc.

Admins, please feel free to delete the attachments if they are too big.

I have used underscores where signals originally had lines above them for ease of type setting

I don't know if this will be of any use to anyone, but I was doing it for myself, so why not share.

Please feel free to post corrections.
The source PDF that I used is also attached, 6522.pdf

PS On the Google Docs version you can just to each section, but the PDF , generated with Word, seems to have lost that!

[lovebug]

nice

[hoglet]

I am revamping my 30 year old BBC Micro emulator and decided the 6522 was a mess.

If you have any questions on the fine detail that's not addressed in the data sheet, take a look at this incredible thread on 6502.org:
- MOS 6522 dissection //NMOS

Dave

[tricky]

My biggest question at the moment is "am I sure I want to update my old emulator?"!
Next week be why half the document is about the shift register, one of the things that I want to support!
I've also been looking through the source of the others and found a few comments on things that need to be checked as the observed behaviour is not explained in the data sheet.
I'm sure that thread will be valuable if I continue the project, something that I'm not good at!

[roland]

The whole emulator was written and tested using chuckie egg, so wasn't the best

I always use Chuckie Egg to test Yarrb boards in my Atoms. If Chuckle Egg runs then everything works fine. Best test program ever

[Kevin Edwards]

If you do go down the path of updating your 6522 emulator then you may want to add the following to your test process:-

Loading and running the original tape images for Nightshade and Lunar Jetman - both by Ultimate Play the Game.

These will really stress test the accuracy of the 6522 emulation - in particular the timer IRQ handling. The tape protection system in both these games makes use of both 6522s and does some quite nasty things to the registers which must be emulated cycle perfect to work - eg. RMW to timers / latches etc. The IRQ handling also has to get things exactly right else the 6522 timers will be wrong and the decryption process will break as it uses the timer values.

The 6522 link you posted is awesome and would have been fantastic to have back in the day when I was torturing the 6522.

[tricky]

Thanks Kevin, I seem to remember Gil stating to write an emulator on the beeb to decrypt probably your code
My goal isn't to be the most accurate been emulator, but to sort the hardware that I make our want to as well as having all the debugging features that I want.
One thing I was thinking of was a scope trace so that I can compare it to an actual scope to help debug in both directions
I'm only doing 2mhz updates, so if order isn't enough, then it won't work! I will need the shift register though and maybe some of the parallel port like modes.