2. When Ground(PL2303) connected to SIM808 moddule (Ground) received the status as OVERVOLTAGE POWERDOWN.Not able to find why this triggered when GRND pin connected each other.
You have to resolve this harware issue first to see the result SIM module on terminal. Test the harware connection and see tha Voltages of PL2303, MCU.
I have tried to communicate the SIM808 module using PL2303 but not able to see the status(RDY) of SIM808 module through PL2303 in PUTTY terminal.
IN SIM300 DATASHEET:
The AT command set implemented by SIM300 is a combination of GSM07.05, GSM07.07 and ITU-T recommendation V.25ter and the AT commands developed by SIMCOM.
Note: Only enter AT command through serial port after SIM300 is power on and Unsolicited Result Code “RDY” is received from serial port. And if unsolicited result code”SCKS: 0” returned it indicates SIM card isn’t present.
If autobauding is enabled, the Unsolicited Result Codes “RDY” and so on are not indicated when you start up the ME
So, you have to set Baud Rate in SIM Module, after successully initialized. i.e. (After hardware issue solved), The terminal will be blank. You have to type AT at Terminal. If you receive OK, then start setting others, like AT+CFUN, Baud Rate, etc. Restart the SIM, will show, RDY and other initialized settings on Terminal.
If you need AT commands (SIM300), let me know. Will send. Hope all AT Commands more or less same for basic functions.
pmk
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Note: When checked the scenario(Status of SIM808 Module) through Arduino not able to found the issue 2(Means received the SIM808 Module status as RDY) without GND(Arduion) pin connected to SIM808 Module(GND).
Without connecting any two device's GNDs, they can't talk each other.
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I suspect that due to this the issue occurred.FYI., Image has attached.
If you suspect this, try to use one diode between TX (PL2303) and RX (SIM Module's) Pins. (Diode Dir -> TX to RX)