acorn atom and acorn system series • Re: AtomMMC Confusion

Thanks Dave. I was trying to help out Prime in this post, and was getting very confused about the different board versions. What really threw me was the schematic on the V2 site and the date of it.

What you've established makes a lot more sense. The schematic that I linked to earlier is clearly the 'fixed V2', which is in effect the V3, and although dated 2010, it would appear that boards with this fix didn't actually appear until 2019ish.

All of the Version 2.x firmware use bit banging use RC4/5 as follows:
- PIC pin 24 (RC5) configured as an input (i.e. MISO)
- PIC pin 23 (RC4) configured at an output (i.e. MOSI)

Roland's Atom 2015, which uses a compatible PIC, also has this wiring, and also runs the 2.x firmware:
https://diy.acornatom.nl/download/atom2015.pdf

Yeah, I looked at that schematic earlier, and that just added to my confusion. It's labelled as MOSI on 24 and MISO on 23 the same as the other V3 schematics, which threw me. However, I now notice that pin 24 is wired to SD card pin 7 and pin 23 is wired to SD card pin 2 (via potential divider), which is opposite to the V3 schematics.

Other than the Atom 2015, I don't think I've ever seen any standalone V2 schematics, with PIC 23 wired through to SD card 7 and PIC 24 wired through to SD card 2 (via potential divider), which is probably the most common board revision out there! But... the board layout drawing on the V2 site does match what you have belled out, so at least that's correct!

Statistics: Posted by KenLowe — Sat Apr 27, 2024 12:30 am

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