Int 1A Fn 80  - Pcjr, Tandy 2500???, Tandy 1000sl/tl - Set Up Sound Multi  [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

Note:  although documented in the 1000TL Technical Reference, the 1000TL
     BIOS has just an IRET for this call

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