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newRPL: [UPDATED April 27-2017] Firmware for testing available for download
07-25-2016, 01:12 PM
Post: #342
RE: newRPL: [UPDATED July-14-16] Firmware for testing available for download
(07-25-2016 11:41 AM)matthiaspaul Wrote:  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 uses 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.

I think both processors behave the same, even other processors of similar family have the exact same SD/MMC on-chip controller. The 50g and 49G+ both have a card detect pin, which as far as I can see it's handled properly during power off (same as all other pins, following the recommended procedure from the S3C2410 manual, also checked the 50g stock rom leaves the pins configured the same as newRPL).

(07-25-2016 11:41 AM)matthiaspaul Wrote:  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.
This is a good possibility, as it makes sense for the UART pins to be disconnected on the 49G+ and perhaps have external resistors on the 50g. Will have to investigate some more.
So far, has anybody else seen excessive battery drain? (can't rule out a defective unit either). My calc lasts more than I expected with a set of batteries during normal use (and not-so-normal too, my SD card burn tests are quite battery hogs).
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RE: newRPL: [UPDATED July-14-16] Firmware for testing available for download - Claudio L. - 07-25-2016 01:12 PM

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