Power input: DC5V or received by a lithium battery input VBAT and GND.
Supports MCU level: 5V / 3.3V for TTL logic
(Such as the common 51 and the for arduino is 5v, STM32 is the 3.3v)
Antenna use: IPEX antenna interfaces, you can use the version PCB antenna or antenna IPEX-SMA- peppers

Pin Description:
5V: power supply pin, the only input DC5V, used to power the board.
V_TTL: access control board microcontroller core target voltage of 5V / 3.3V (according to its own microcontroller is much to distinguish kernel v), this pin is used to convert the GSM module board TXD and RXD for the corresponding TTL logic.GND: power supply ground
TXD: send pin serial port module, TTL level (not directly connected to RS232 level)
RXD: receive pin serial port module, TTL level (not directly connected to RS232 level)
DTR: Data Terminal Ready
SPKP: Core Audio output pin
SPKN: Core Audio output pin
MICN: Core Audio input
MICP: Core Audio input
RI: Ring core pin tips
VRTC: RTC pin external battery
GND: power supply ground
PWR: This pin can turn down or turn off the module
GND: power supply ground
VBAT: lithium battery input pin, 3.3v-4.4v