I am in the same boat and trying to figure out how to access the CatM base's modem.
I have Core2 (AWS), IoT Base Cat-M.
I disconnected the battery (M5GO) from the Core2, then connected Core2 with the IoT Base CatM using the male/female headers on both boards.
If I power up the CatM base, the Core2 does power up. But the example program cannot communicate with the modem at all.
The example program listing is also given on File -> Examples ->M5Core2 -> CatM_GNSS_7080 -> MQTT
I appreciate any pointers for help please.
I just want to know if any additional steps are needed to perform AT commands to the modem. (SerialAT is defined as Serial2 in the program listing) But we get UART connect errors etc....