common pin definitions

Pin Functions
VBUS Power supply from USB port
VIN Power input up to ~18V
3V3 on board 3.3V LDO output
DTR UART DRT pin
~RI UART RI pin
RXD UART receive via logic shifter
TXD UART send via logic shifter
PEN on board dcdc power supply enable default on
GND board power supply ground
RST gpio_control_reset

obseleted

pin function
3v3 or bat direct system power supply
vin external high voltage supply
gnd Power Ground
p_en on board power chip enable pin
logic_pwr logic power level supply
rx RXD
tx TXD
boot M2M module boot pin
.. ..

ref