Battery reads about 3.2vdc, and I tried a fresh one to be certain.
I traced back each lead of the DS12885 and all show continuity. I replaced the 74LS32 and 74LS02 that do the address decoding, and also tried "74F parts with no improvement. I swapped 8088-1 processor, and also dropped the clock rate to 5mhz. I've added and removed wait states for I/O. I've resoldered the entire board.
My only thought at this time is that perhaps I have a bad batch of xtals. I've ordered a few replacements to try.
Ah well, it has to be something simple!
- Gary
On Wednesday, July 16, 2014 3:43:28 PM UTC-4, Vince Mulhollon wrote:
Battery voltage pin? From memory that part was like that famous memory controller chip that got all wound up if the battery voltage was wrong. And it was picky, none of this connect to Vcc stuff, it had to be almost 3V, exactly, or it was super unhappy. If its oscillating it must be OK-ish unless the battery is super low. Maybe just barely enough to oscillate but not work...
Some kind of lockout circuitry would get confused, like the delta between Vcc and Vbatt had to be about two volts or it assumed power was lost and wouldn't talk, even if Vcc was a perfectly good 5V. So a dead battery at 1V means no talking even if you'd think it should talk because Vcc is a perfectly good 5V.
Thats all I got on that chip.