Int 14 Fn 164D  - Digiboard - Ccb Command - Set Transmit Mid-water Mark    [S]

   AX = 164Dh
   BX = new mid-water mark
   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=164Ch,AX=164Eh,AX=164Fh