Int 14 Fn 164C  - Digiboard - Ccb Command - Set Xon/xoff Characters        [S]

   AX = 164Ch
   BL = XON character
   BH = XOFF character
   CL = byte 1
   DX = port number (00h-03h) (04h-43h for XAPCM232.SYS)

Return: AH = status
       00h successful
       80h error
       FFh error

See Also: AH=16h"Digiboard",AX=164Bh,AX=164Dh