Int 1A Fn 80  - PCjr - Set Up Sound Multiplexor                            [s]

   AH = 80h
   AL = 00h source is 8253 channel 2
        01h source is cassette input
        02h source is I/O channel "Audio IN"
        03h source is sound generator chip

See Also: AH=7Fh,AH=83h