Greetings:
A recent thread in this N.G. addressed the issue of dead batteries in CMOS Clock/Calendar/RAM devices such as the Dallas DS1287, DS12887, Twinhead TH6887A, and others; some of these devices are no longer available as new stock and old stock is often also unusable and for many there are no equivalent replacements. Surgery to permit attaching external backup power sources is possible but not documented (to any searchable degree) on the 'Net. I describe surgery on the TH6887A on this page:
This device employs no external power source for the RAM and clock so a dead battery means the RAM doesn't appear on the bus and clock settings are ignored.
Please e-mail me with any data on the internal construction of other such devices and I will include them on the site.
Regards,
Michael