Detecting presence of SD-card on HP-50g

[Claudio L.]

(07-15-2021 11:53 PM)DavidM Wrote:  

(07-15-2021 08:28 PM)ijabbott Wrote:  The SD card power and ground pins are designed to make connection before other pins on insertion, and to break connection after other pins on removal, so indeed power will be applied before the other pads are making contact if the calculator is on during insertion. (I don't know if that is actually a problem for the calculator.)

I was sure that I had read somewhere that the 49g+/50g should be turned off before inserting or removing the SD card. A quick look through the User's Manual for both of those devices doesn't seem to mention that, though. I still may have read it somewhere else, but that's where I thought I had gotten the info. So my memory is less accurate on this topic than the card currently inserted into my calculator...

Furthermore, after testing the above program with the card being inserted/removed without an intervening power cycle, it seems to still work as designed. Apparently the Kinpo O/S still knows when the card status has changed, even without a power cycle. So I'll amend the post to mention that stipulation may not apply after all.

The Kinpo OS has no caching of any kind, does not delay writes or keep any state in RAM that could be compromised if you pull the card.
Having said that, if you pull the card WHILE it's still writing on the card you will end up with a damaged file system.
In addition, some SD cards have INTERNAL caching and delayed writing, so turning off the calculator or pulling the card quickly after writing to it also risks ending up with a damaged file system.
So while you don't need to turn the calculator off, you do need to be patient and wait several seconds after you write to the card before you cut power to it. Cutting power means: turning the calculator off, pressing the reset button, pulling batteries, pulling the card out.