I took it on myself to develop a master transmit / receive library for the two wire interface (I2C). Then port this to an interrupt service routine.
Problem is this. If I include the wire.h library my code works. I don't even have to call any functions from the library. Just include it.
I'm having trouble getting low level help with the TWI interface. So I think I'll have to use the wire library.
I never got far enough on my own to implement an ISR.