my recollection is that for low voltage programming you have to program it for that before you can program it with your code
also that there may have been other issues or difficulties, are either of those fears true ?
can you outline the steps to do low low voltage ISP with a virgin blank chip soldered to the board ?
am using 16F1828 for this one and MEL U2 programmer
in the meanwhile i made some other progress on the original question here:
it seems that Microchip makes MCP131 (i was using MCP130, '131 is pin compatible) which is specifically for this issue and has 14V withstand on the open drain,
they also show a mandatory series resistor, nominal 1k (which means /MCLR pullup would need to be >10k
this is all good but what i did not mention earlier is that the VPP/MCLR line is also going to a bunch of MCP23017 reset pins which i have isolated for the moment, so i guess i would need a clamp diode on those and hope the U2 programmer can delivered the required current
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