HP97 The journey begins

[teenix]

Hi all,

I've just created a new version of the HP-67 replacement CPU board and this one has Constant Memory. This change in hardware should also suit the HP-97 CPU board.

The main problem with adding this feature was that due to the original 67 hardware design, a wire would have to be added to connect the CPU board to the battery so the memory can stay alive. Unfortunately, this method means the PIC processor also has to stay "alive", although in sleep mode. Even so, some current from the battery would always be drawn. The wire connection also interferes with board removal, although a connector could be used. I didn't really want to solder a wire to the keys circuit board either.

To avoid those issues, the new CPU board can keep its memory alive indefinitely without a battery. I just have a bit more testing to do to make sure the HP microcode can work with it under all working conditions, but so far it seems ok.

cheers

Tony