INT 14 - IBM/Yale EBIOS SERIAL I/O - SET OUTGOING MODEM SIGNALS
AH = FBh
AL = modem control register
bit 0: data terminal ready
1: request to send
2: OUT1
3: OUT2
4: loopback
bits 5-7 unused
DX = port (00h-03h)


14FB - IBM/Yale EBIOS SERIAL I/O - SET OUTGOING MODEM SIGNALS