Function 21h    Power-On Self Test (POST) Error Log	(PS/2 50+) 
entry   AH      21h 
	AL       00h    read POST log 
		 01h    write POST log 
			BH      device ID 
			BL      error code 
return  CF      set on error 
	AH      status 
		00h    OK 
		       BX      number of error codes stored 
		       ES:DI   pointer to error log 
		01h    list full 
		80h    invalid command 
		86h    unsupported 
note    The log is a series of words, the first byte of which identifies the 
	error code and the second the device.