INT 21,44,3 / IOCTL,3 - Write to Character Device
AH = 44h AL = 03 BX = handle CX = number of bytes to send DS:DX = pointer to data buffer on return AX = number of bytes written if CF clear = error code if CF set (see DOS ERROR CODES) - see bit 14 if IOCTL function 00h to determine if driver can support IOCTL control strings