Hi Ben,
if you need the clock signal to transmit data it is possible to use the serial port in mode 0. RXD (P3.0) is used to transmit the data and TXD (P3.1) for the clock. The rate is fixed to the crystal frequency divided by 12. A second way is to implement it by software. Then you can use any unused pin. In the first case data is transmitted one byte at a time.

Best regards
Christian