Since the merging of topics I'm even more confused than before.
I thought you wanted a short hand way to send 1001 by typing a, not 1001. Your thought was to do that in the pc, type a, send 1001. Mine was to do it in the Arduino, type a, send a, use 1001 internally. I'm not clear on where the fpga fits in.
Give us a block diagram of what's going on here?