I want to do In-System programming for an ATmega48 with and AVRISP MKII.
During programming I need to isolate the target board VCC (3.3V) from the programming voltage because the programmer cannot provide power for the complete board. The target board is unmounted, so I cannot use the target board power itself.
A series diode for isolating board VCC and programming VCC consumes about 0.4V, which is to much.
Does anybody have an implementation idea using a FET or similar instead of the series diode?
I will implement series resistors for MISO, MOSI and SCK. I did not find any recommendation for resistor values. Any recommendation from the forum?