...
UART at 2.8V
Pads on top side of tracker (Next to SIM holder, with pin 1 labeled 'VBAT')
pin 3: UART_GND - same as VIN_GND (ground for VIN which is the external power supply to the tracker)
pin 4: TRACKER_TX (tracker TX on this pin)
pin 5: TRACKER_RX (external device TX on this pin)
...
UART protocol
115200 bit/s
8N1
no flow control
...