Bug #4211
closedfind solution for inverted polarity of SIMx_DET (SIM present) switches and their altered pin designation on some modems for 2nd SIM
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Description
This ticket is about a needed polarity inversion of the SIM detect switches and a partly re-designation of the respective pins.
- The modems tested here with the M.2/NGFF prototype (ME936, EM7565) both make use of pin 40 and pin 66 (SIM_DETECT_1) of the M.2 connector, but only the EM7565 is capable of running a 2nd SIM card. This results in a different usage for pin 40: on EM7565 it is SIM_DETECT_2, but on ME936 it is I2C_SCL! This also means a change in pin type (input vs. output).
- The selected SIM card holder uses N.O. contacts to detect SIM presence; they now connect to GND when SIM is inserted. For the modems tested, this means inverted polarity: both recognize low as 'not present'. For the respective primary (or only) SIM they mention an internal pull-up, so Sierra recognizes even a floating SIM_DETECT input as "SIM present". Huawei claims to detect edges, not levels on that input (for 'hot swapping')...
As laforge mentioned, the SIM_DETECT signal can be considered a rather 'esoteric' signal as the SIM can be polled anyway, we might drop the SIM_PRESENT logic completely. However, Sierra claims their primary SIM_DETECT (pin 66) a "required signal"... During testing the prototype, contact legs were isolated from each other to simulate constant SIM presence.
What do you think on how to solve these two contraints together? More jumper to be more flexible? Drop the SIM_DETECT contacts' connections at all?
Files
Updated by mschramm over 4 years ago
- Subject changed from find solution for inverted polarity of SIMx_DET (SIM present) switches and their altered designation on some modems to find solution for inverted polarity of SIMx_DET (SIM present) switches and their altered pin designation on some modems for 2nd SIM
Updated by laforge over 4 years ago
Hi,
On Tue, Sep 17, 2019 at 05:10:18PM +0000, mschramm [REDMINE] wrote:
- The selected SIM card holder uses N.O. contacts to detect SIM presence; they now connect to GND when SIM is inserted. For the modems tested, this means inverted polarity: both recognize low as 'not present'. For the respective primary (or only) SIM they mention an internal pull-up, so Sierra recognizes even a floating SIM_DETECT input as "SIM present". Huawei claims to detect edges, not levels on that input (for 'hot swapping')...
That inversion could be resolved by connecting the switch to some positive voltage rail (1.8V?)
instead of GND. If you know of modems that are low=inserted and other modems that are high=inserted,
then we need to add a transistor stage and jumpers to select.
What do you think on how to solve these two contraints together? More jumper to be more flexible? Drop the SIM_DETECT contacts' connections at all?
I think we should have a series jumper for the "I2C" case and switch polarity as described
above.
Updated by mschramm over 4 years ago
- File NO-switch.jpg NO-switch.jpg added
- File SIMport2.jpg SIMport2.jpg added
laforge wrote:
That inversion could be resolved by connecting the switch to some positive voltage rail (1.8V?)
instead of GND.
...and some resistors, understood. I did it as on the first image (NO-switch.jpg) with 4k7/47k, given, that the internal PU will be (likely much) weaker than 47k.
If you know of modems that are low=inserted and other modems that are high=inserted,
then we need to add a transistor stage and jumpers to select.
No one found so far, so we can skip this.
I think we should have a series jumper for the "I2C" case and switch polarity as described
above.
OK, but then let's see whether there would be enough space for bringing all five SIM2 card-related signals (see 2nd image SIMport2.jpg) to a 2x5 header with jumpers (as default for 2nd SIM or open for breaking out these signals).
Updated by mschramm over 4 years ago
- Status changed from In Progress to Resolved
- % Done changed from 0 to 100
The current design now incorporates an additional 2x5 header for the USIM2 signals, serving as a breakout header for modems which don't support a 2nd SIM but have different signals on these pins. For modems which support two SIMs, this header must be bridged with five jumper. - I hope this covers the cases needed.
