[Pat Fairbank]

For receiving on the serial port to work you need to have ENABLE_SERIAL_PORT_ONE_RX defined and to call Init_Serial_Port_One() in the initialization, but I'm assuming from the content of your post that you've got that covered.

Are you confident in the integrity of your null modem cable? If you're receiving input on the computer terminal, that's fine, but that's presumably with a different plain serial cable. Try hooking up the slave to the computer and sending the '@' from the terminal.

Also, if I were trying to debug this problem I would put some temp code to flash the lights directly in the serial port rx interrupt handler in user_routines_fast.c, just to verify that the serial port is receiving independently of what's being sent.

Lastly, when you say "null modem cable", you do mean a male-male serial cable that has the TX and RX pins swapped along the length and not just a normal serial cable with a gender-bender, right? Just checking.