INT 14 - Digiboard - CCB COMMAND - SET XON/XOFF CHARACTERS                      
	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
SeeAlso: AH=16h"Digiboard",AX=164Bh,AX=164Dh