INT 15,21 - Power On Self Test (POST) Error Log (PS/2 except 30)

	AH = 21h
	AL = 00 read POST error log
	   = 01 write error code to POST error log
	BH = Device code  (if write)
	BL = Device error  (if write)

	on return
	CF = 0 if successful
	   = 1 if in error (AH contains code)

	if reading POST error log:
	   AH = 00h if successful
	      = 80h (PCjr and PC)	 = 86h for all other machines
	   BX = number of POST error codes stored
	   ES:DI pointer to POST error log

	if writing POST error log:
	   AH = 00h if successful	 = 01 POST error log full
	      = 80h (PCjr and PC)	 = 86h for all other machines