Function 00h    Turn Cassette Motor On			(PC, PCjr only) 
entry   AH      00h 
return  AH      86h     no cassette present 
	CF      set on error 
		AH      error code 
			00h     no errors 
			01h     CRC error 
			02h     bad tape signals 
			        no data transitions (PCjr) 
			03h     no data found on tape 
			        not used (PCjr) 
			04h     no data 
			        no leader (PCjr) 
			80h     invalid command 
			86h     no cassette present 
			        not valid in PCjr 
note    NOP for systems where cassette not supported