[Ovmsdev] Cannot reset simcom stuck in PoweringOn state without removing module power

Craig Leres leres at xse.com
Mon Nov 18 02:31:55 HKT 2019

On 2019-11-17 04:11, Michael Balzer wrote:
> I also saw this & can also reproduce this on my workbench.

What is the method to induce the problem?

> Mark, it seems we've got a hardware flaw here: EGPIO output port 0 (MDM_EN) is connected to transistor Q2 base via R16 without any pull-up. As the EGPIO ports
> are open drain, that can only work by chance. Maybe R16 was meant to be the pull-up, i.e. be connected to +3.3V, and MDM_EN should be connected directly to the
> transistor base?
> I've verified this by checking the voltage level at MDM_EN & PWRKEY. When setting the port to 1, MDM_EN only rises for a very short time (too short for my
> multimeter to tell), and PWRKEY only drops very briefly. The modem needs PWRKEY low for at least 180ms to power up and at least 500ms to power down.
> Manually pushing S1 reliably switches the modem on/off.
> Maybe a fix for existing boards could be adding a pullup resistor at the transistor base?

I could try this if you suggest a value (and perhaps mark up a schematic?)


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