GSM 900A modem not responding to AT commands I am using GSM 900A modem which requires 5V Supply. I am connecting it to Arduino UNO. I am giving supply to modem by arduino 5V and GND pin. I am connecting RXD pin to TX(pin 1) of arduino TXD pin to RX(pin 0) of arduino and GND to GND of arduino i.e. pin 14. I am running the basic example codes but GSM is not responding. I have also tried other softwares like Putty but I am unable to write any AT command Please help me. When I tested the modem using this code:
/*

 This example tests to see if the modem of the
 GSM shield is working correctly. You do not need
 a SIM card for this example.

 Circuit:
 * GSM shield attached

 Created 12 Jun 2012
 by David del Peral
 modified 21 Nov 2012
 by Tom Igoe

 http://www.arduino.cc/en/Tutorial/GSMToolsTestModem

 This sample code is part of the public domain

 */

// libraries
#include &lt;GSM.h&gt;

// modem verification object
GSMModem modem;

// IMEI variable
String IMEI = &quot;&quot;;

void setup() {
  // initialize serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }

  // start modem test (reset and check response)
  Serial.print(&quot;Starting modem test...&quot;);
  if (modem.begin()) {
    Serial.println(&quot;modem.begin() succeeded&quot;);
  } else {
    Serial.println(&quot;ERROR, no modem answer.&quot;);
  }
}

void loop() {
  // get modem IMEI
  Serial.print(&quot;Checking IMEI...&quot;);
  IMEI = modem.getIMEI();

  // check IMEI response
  if (IMEI != NULL) {
    // show IMEI in serial monitor
    Serial.println(&quot;Modem's IMEI: &quot; + IMEI);
    // reset modem to check booting:
    Serial.print(&quot;Resetting modem...&quot;);
    modem.begin();
    // get and check IMEI one more time
    if (modem.getIMEI() != NULL) {
      Serial.println(&quot;Modem is functoning properly&quot;);
    } else {
      Serial.println(&quot;Error: getIMEI() failed after modem.begin()&quot;);
    }
  } else {
    Serial.println(&quot;Error: Could not get IMEI&quot;);
  }
  // do nothing:
  while (true);
}

I am getting this output on Serial Monitor for 9600 baud rate:

Starting modem test...ERROR, no modem answer.
Checking IMEI...Modem's IMEI: 0
Resetting modem...Modem is functioning properly
The modem library does not communicate on pins 0 and 1. Check the reference library and tutorial. It should be pins 2 (RX) and 3 (TX). Reset is pin 7. The configuration may be found in GSM3IO.h. https://github.com/arduino/Arduino/blob/master/libraries/GSM/src/GSM3IO.h. See also https://www.arduino.cc/en/Main/ArduinoGSMShield