Hi Matthew,

I looked over the datasheet and can't see any way to take control over this pin if the USART is enabled. If you're planning on triggering the triac with low pulses you might get away with this pin afterall. If you transmit $ff that will simply be one low pulse, 1/baudrate long(1/9600=0.1ms). If this is not possible, you need to disable the USART and go softwareserial instead.

/Ingvar