Hello @felmue

I got it working now. The PWRKEY pin needs to be low for a minimum period of 1 second and a maximum period of 12.6 seconds. After this the PWRKEY pin needs to be put high again, otherwise unpredictible things might happen. Subsequently there is a minimum time defined in which the UART is ready. This minimum time equels 1.8 seconds after power-on. (table 8, power on timing and electronic characteristic).

So my final (working) code is:

pinMode(GPIO_NUM_27, GPIO_MODE_OUTPUT);
digitalWrite(GPIO_NUM_27, HIGH);
delay(1000);
digitalWrite(GPIO_NUM_27, LOW);
delay(800);

Hello @felmue

Thank you, Unsolicited codes are clear now. But I am still wondering about the 5 seconds on, 5 seconds off part. Very often I also don't get any reaction from any AT command with the same software. I am using https://github.com/m5stack/M5_SIM7080G as an example.

I changed the include to M5Core2.h and the pins to RX=35 and TX=0. But communicating with AT commands happens rarely or not all. Are there any other things that I should check to make this work?

I made a combination of a M5core2 module with SIM7080G CAT module. I am able to send AT commands and receive a response. However it turns out that a lot of AT commands do not come through. Further testing reveals that there is a 5 second up and 5 seconds down schedule. I send an AT command every second to the device, I get 5 responses and after that 5 timeouts. Than again 5 responses and 5 timeouts. After a while I suddenly get a +CFUN and +CPIN reponse while never asking for it.

Is there a process active that blocks communciation every 5 seconds for a period of 5 seconds?
Where do the +CFUN and +CPIN reponses come from?