INT 6B - NPC NCSI EXTENDED SERIAL I/O - WRITE DATA ON A VIRTUAL CIRCUIT AH = 18h AL = virtual circuit number CX = number of characters to send ES:BX -> buffer containing characters to be sent Return: CF clear if successful CF set on error ??? Note: this function is also supported by TelAPI, which always returns CF clear and AL=30h SeeAlso: AX=0000h,AH=12h,AH=19h