INT 21 - DOS 2+ - IOCTL - WRITE TO CHARACTER DEVICE CONTROL CHANNEL
        AX = 4403h
        BX = file handle referencing character device
        CX = number of bytes to write
        DS:DX -> data to write
Return: CF clear if successful
            AX = number of bytes actually written
        CF set on error
            AX = error code (01h,05h,06h,0Dh) (see AH=59h)
Notes:  format of data is driver-specific (see below for some specific cases)
        if the file handle refers to "4DOSSTAK", the 4DOS (v2.x-3.03)
          KEYSTACK.SYS driver will push the specified characters on the
          keyboard stack; similarly for "NDOSSTAK", the NDOS KEYSTACK.SYS
          driver will push the characters onto the keyboard stack
SeeAlso: AX=4402h,AX=4405h,INT 2F/AX=122Bh,INT 2F/AX=D44Dh