INT 1A - PCjr, Tandy 2500???, Tandy 1000SL/TL - SET UP SOUND MULTIPLEXOR        
	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(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware.  The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. has just an IRET for this call
SeeAlso: AH=7Fh,AH=83h