I guess there is no point reading past this unless you have a solution. But it's a free forum. :?
It seems I have lost nSRST (pin 6 of the JTAG header) therefore no ISP, PDI or DW functionality anymore :evil: JTAG seems to work as it doesn't use that line unless the JTD bit has been written to and the target cannot be reset for debugging/programming.
I have traced the signal to the SPST switch (top MAX312) and the nSRST switch input is idling at a suspicious 2.8V jumping briefly to 5V when trying to connect. The nSRST pin does not budge, it should go low when attempting ISP.
Does anyone know where the switch input is coming from? Is there (hopefully) a level shifter chip that might have blown up? If the actual M128 pin is blown then it will be pretty much beyound repair. :( :(