Int 1A Fn 8100  - Tandy 2500, Tandy 1000l Series - Digital Sound - Instal  [s]

   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"