HP48GX RAM card design

[pdo]

(06-22-2017 03:04 AM)mfleming Wrote:  I'd love to see if this design would work in an SX! I pulled mine from mothballs a while back, along with a TDS memory card. It had a CR2016 holder that allowed the coin cell to be replaced while the card was in the SX so that RAM content was not lost. Perhaps in lieu of programmatic bank switching, the address switches could be moved to the interior to make room for the battery?

Well, it may not be as much of a problem as you might think. I realized that my testing of the C1 & C4 battery change capacitors was done with the faulty board, and that the fault was probably invalidating my battery change tests. So today I retouched some of the solder joints on the misbehaving board and this evening was able to confirm that the board seems to behave correctly now :-)

I then redid my battery change tests:-
1. Take the board out of the calculator.
2. Remove the battery from the board, hold for 10 seconds, then reinsert battery.
3. Put the board back in the calculator and check objects in all 4 ports are still okay.

I did this three times and am happy to report that the test passed each time. Not exhaustive I know, but encouraging non-the-less.

I now feel an edit of the README coming on...

Paul