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newRPL: [UPDATED April 27-2017] Firmware for testing available for download
07-25-2016, 11:41 AM (This post was last modified: 07-25-2016 11:05 PM by matthiaspaul.)
Post: #341
RE: newRPL: [UPDATED July-14-16] Firmware for testing available for download
(04-12-2016 01:17 PM)Claudio L. Wrote:  
(04-12-2016 10:09 AM)Nigel (UK) Wrote:  I've left the calculator turned off for about 2 hours and the current settled at about 4 mA. Removing the SD card causes the current to jump up to 10 mA. Re-inserting the card causes the current to drop back to 4 mA again, even before the card is properly seated. Simply having the card mostly in without pushing causes the current to drop.
Good info, thanks. I'll look into the SD card pins.
I don't have any special insights into the circuitry of the HP 49g+/50g (do we have a schematic available somewhere?), but to me this looks as if the interface has no pull-ups (or pull-downs). SD cards have internal pull-ups, so this isn't an issue for as long as a card is inserted, but without a card the interface lines may start floating and thereby cause unwanted currents to occur in the CMOS ports.
Some microcontrollers can keep internal pull-ups (or pull-downs) enabled in sleep modes, whereas others would disable them in sleep. I haven't checked the datasheets, but it might be worth looking into what applies to the processors used in these calculators.
Also, I seem to remember that the HP 49g+ uses a Samsung S3C2410X01, whereas the HP 50g uses a S3C2410A. Perhaps the minor differences between these revisions happen to affect this area?
Or does the HP 50g use actual resistors, whereas they are not populated in the HP 49g+?

The above description could be read also as if the behaviour would occur even before the SD card actually makes electrical contact with the card holder. If so, does the card holder feature a "card detect" switch? While for most card holders the metal frame (if any) is connected to GND, I have also seen card holders, where the frame is connected to the switch contact, so without any pull-up or pull-down capacitive coupling might cause the corresponding input line into the processor to start floating. It does not explain different behaviour between the HP 49g+ and 50g, though.

Regarding other differences between the HP 49g+ and the 50g: The HP 50g has a 3.3V TTL serial port, whereas IIRC the HP 49g+ has not. Perhaps the TTL RX line in the 50g has a physical pull-down resistor (and therefore isn't specially treated in the firmware), whereas it is floating in the 49g+?

Hopefully, these "loose ends" can help tracking down the issue.

Greetings,

Matthias


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RE: newRPL: [UPDATED July-14-16] Firmware for testing available for download - matthiaspaul - 07-25-2016 11:41 AM



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