U137 Modem Resets Immediately After Entering PSM Mode

Safeware

I am currently testing LTE and GNSS functionality using the M5Stack U137 modem.

While attempting to reduce power consumption by enabling PSM (Power Saving Mode), the modem consistently resets immediately after entering PSM, causing PSM to be exited unexpectedly.

I would like to ask whether any additional configuration or specific settings are required to ensure stable operation in PSM mode on the U137 module.

Below are the AT command sequences I sent and the corresponding log records for reference.

09:32:20.651 << +CPSMSTATUS: "ENTER PSM"
09:32:24.457 << RDY
09:32:25.021 << SMS Ready
09:32:26.478 << +CPSMSTATUS: "EXIT PSM"

felmue

Hello @Safeware

you probably are not missing anything from the software side. The issue most likely is caused by the PWRKEY hardwired to the STATUS output of the modem. This 'trick' is used to auto-start the modem. However it also causes the modem to wake-up from PSM immediately.

See modem schematics here.

From SIM7070_SIM7080_SIM7090 Series_Low Power Mode_Application Note_V1.02 found here.

Section 3.1 PSM Wake-up states:

Wake-up conditions:
1) T3412 timer is expired
2) Pulling PWRKEY to low level

If above is not the issue, then there are some points to check:

have you tried with both connection types: CatM and NB-IoT?
is GNSS turned off? SIM7080G can only used WWAN or GNSS, but not both at the same time.
Is your SIM7080G using the latest firmware?
Does your provider actually support PSM?
Is your power supply able to deliver the necessary current? Resets often are caused by too weak power supplies.

Thanks
Felix