Initialization

1. Write the required value for P to FIFO_INIT.
2. Activate reset by writing to ACTIVATE_RESET.
3. Wait at least 200 ns.
4. Deactivate reset by writing to DEACTIVATE_RESET.
5. Enable required interrupts by writing to INTRPT_CTRL_STAT_REG. (Write 7 to enable all 3 interrupt sources: NOSIGNAL, NODATA and control-char)
   (NOTE: the data FIFO-flag interrupts are enabled by inserting onboard jumpers, one for the XINTA interrupt, one for the XINTB interrupt, but probably these interrupts won't be used when control character interrupts are used, unless to detect an alarm situation ('FIFO too full')).