Firmware Revisions (ROM XB224):

To show version hold down the 8 and 9 buttons then turning the power on:

Version 1.0  released 22-APR-87 
Version 1.1  released 25-JUN-87 
Version 1.2  released 31-JUL-87 
Version 1.3  released 27-OCT-87 
Version 1.4  released 25-MAR-88 
Version 1.5  released 17-JUN-88 (Servicing ROM XB224007)
Version 1.51 released ??-???-?? ( Part Number  XB224G01) Final Version!