my M66 module sometime falls into state, where I can’t restart it from.
After 10 x sending AT to M66 without response, I try to restart module - see picture
Pull PWRKEY pin for 870ms down, then wait 13 sec and try to switch on.
However VDDEXT voltage doesn’t change, no NORMAL POWERDOWN on serial line appears.
Communication with modem is stuck, and only way how to fix is power down / power up.
However netlight pin stil shows that modem is attached to GSM network.