I've connected the arduino Mega with my SIM5320E as below:
SIM5320E <--> Power Source / Arduino Mega 2560
5V <--> 5V (Power source)
GND <--> GND (Power source)
VMCU <--> NOT CONNECTED
STXD <--> RX217 Arduino
SRXD <--> TX216 Arduino
GND <--> GND
But I am unable to send AT command successfully.
Is there anyone able to advise on this?