I've assembled some PCBs that I had made, and I'm unable to get the ATmega2560 to respond to programming via the ICSP header. On the third board I'm trying, I have soldered on only the MCU, the ICSP header and a reset pull-up resistor.
Here are the things I've checked:
- No shorted pins
- Supply voltage to all the Vcc pins
- Ground connection to all the GND pins
- MOSI, MISO, SCK and RESET all have continuity from the header to the pins
- The programmer works (tested with an Arduino Mega 2560)
- That ATmega2560s are shipped with the fuse bits set to use the internal oscillator
The DSO shows RESET going low, clock, and MOSI coming in, but no MISO goes out.
What else could I check?