INT 1A - Tandy 2500, Tandy 1000L series - DIGITAL SOUND - INSTALLATION CHECK    
	AX = 8100h
Return: AL > 80h if supported
	AX = 00C4h if supported (1000SL/TL)
	    CF set if sound chip is busy
	    CF clear  if sound chip is free
Note:	the value of CF is not definitive; call this function until CF is
	  clear on return, then call AH=84h"Tandy"