DosFoxDespite the failure of the #MacCharlie, I've at least been able to build a #ShimIWM, as my boards arrived today.
I'm pleased to say it works!
I made a stab at explaining how the #ShimIWM [SCHWIM] works!
https://github.com/DosFox1/Shim-IWM/tree/main
I hope this makes sense, full warning - I am almost certainly wrong about how it works, but it works!
GitHub - DosFox1/Shim-IWM: A simple electronic "shim" to replace an Integrated Woz Machine in a Macintosh. It contains just enough hardware to pass the initial boot check, and boot into Mac OS via SCSI.
A simple electronic "shim" to replace an Integrated Woz Machine in a Macintosh. It contains just enough hardware to pass the initial boot check, and boot into Mac OS via SCSI. - DosFox1/S...
A nice single chip implementation of the #ShimIWM - this is a 74ls541, which is an octal buffer that needs two enable lines - one is connected to A0 of the IWM (pin 3 of the IWM. Sometimes noted as A1?) and the other is connected to /DEV (pin 7).
The data is still 0xDF (11011111 in binary) which is enough to get the system to boot into SCSI