Int 14 Fn 05  - PC-mos/386 V5.01 $serial.sys V5.04 - Change Port Protocol  [S]

   AH = 05h
   AL = bit 7: set to enable/disable CD monitoring, clear to set protocol
        ---bit 7 set---
        bit 4: CD monitoring enabled
        bit 5: automatic restart enabled
        ---bit 7 clear---
        bit 0: receive XON/XOFF
        bit 1: transmit XON/XOFF
        bit 2: DTR/DSR
        bit 3: RTS/CTS
   BH = new XOFF character
   BL = new XON character
   DX = port number

Return: AH = FFh if invalid protocol

See Also: AH=00h,AH=04h"SERIAL",AH=06h"PC-MOS"