GSM Modem/Module not responding to AT commands after firmware Upgrade??

I get a lot of queries about this issue, so I thought I should write a small post about it. For example the latest one was

Hello Muhammad,
I recently update SIM900 to firmware 1137B12SIM900M64_ST.cla using “Simcom – sim900 Customer flash loader V1.01″ at the baud rate 1498000. Everything went perfectly like but after I restart the module I get “þIIIIþþþ” response from SIM900 at 115200 baud rate, I could not get any AT commands working. Kindly do help me.

Some modems support AutoBaud by default. Auto Baud feature allows the modem to be used with any baud rate, and for this to be used the Modem waits for a input string “ATr” it uses this string to detect the baud rate being used. As the manual describes the modem when in Auto Baud will be looking for this string after it is powered and this should be in CAPS otherwise modem wont be able to detect the correct baud rate. Sim900 has the auto baud by default. Some modems don not support Auto Baud so for these modems after the firmware has been updated, you should use the default baud rate, 9600 and 115200 are the most common.

RECOMMENDED READ  latest enhance firmware for SIMCOM SIM900 module (1137B03SIM900M64_ST_ENHANCE )

if you want to fix or change the baud rate you should use the AT+IPR command. For example if you need to fix it to 4800.


Dost Muhammad Shah

Dost Muhammad specializing in Embedded Design, Firmware development, PCB designing , testing and prototyping. He enjoys sharing his experience with others .Get in touch with Dost on Twitter or via Contact form


159 thoughts on “GSM Modem/Module not responding to AT commands after firmware Upgrade??

  1. Hello Muhammad,

    Pls find below a small write about dial up connection problem I am facing…

    I have USB GSM GPRS Modem using Neoway M660A module.

    I also have a tool that we use to establish internet connection using a Dial up Connection.

    The tool establishes the net connectivity using Windows Rasdial command. The tool also Pings my server every 30 Sec to check for connectivity. This is working absolutely fine.

    The connection once established will work for 2 hrs / 3 hrs / 30 min / 5 hrs and so on. During this time if I want to manually disconnect the net connectivity I am able to do and also reestablish the connection as and when required. This functionality is working fine.

    However, sometimes the connection is lost on its own / Ping Test fails, for some reasons not known to me. I am not able to RE ESTABLISH the net connectivity without re-starting the PC.

    My observations are as under:

    1. Once connection is lost, the tool is able to detect the same.

    2. I am trying to execute the rasdial / Disconnect command to disconnect the same. However as I understand this rasdial / disconnect works only when connection is there but since our connection is already lost, this rasdial / disconnect command is not getting executed.

    3. When v try to re establish the connection using rasdial / connect again, we get a message “Access Denied” – Possibly an indication that Com port is not released as connection is lost on its own.

    I am looking forward for suggestion / recommendation from you that I can possibly try out to be incorporated in the tool so that our problem of re establishing the connection when it is lost / ping test fails is successful and I am able to have seamless net connection all through out the time when PC is powered on.

    Requesting you to pls share your suggestions at the earliest.


      1. hello sir i am using sim 900a module and supplying 5v and 2 amp to this but it is not getting network… when it try to catch network the power led just dim and aftr that it glows and status led continuously blinking within second plz help me in this and can i use it in pakistan?

  2. Hi which firmware do i need for S2-105MB-Z160K SIM800 module ? i doesn’t respond to any at command but i can flash the chip

  3. hi guys,
    i was searching about the same issue , i got SIM808 and it was working so normal .
    yesterday , i saw no responding at all. i checked the cables is the same , then i tried to call my number and its calling me !!
    then i tried to write Serial.available and its print the y character.
    is anyone reach the solution illuminate us please.

  4. hello sir I intertefaced the GSM AND GPS module to the Arduino mega but my GSM inbuilt max232 was heating too much plz healp sir

        1. Yes. Seems to me like your module is in auto-baud mode. It needs to know what baud-rate you are communicating at.

          1. I read something about it, but couldnt fix it.
            On Termite and puTTY I tried many baud-rates on them. On their own configs. 1200. 2400.9600… To 460800.
            At the same time, couldnt sent AT+IPR to de module. It doesnt respond to any command and every second the terminal software is populated with that characters. It worth to mention that the characters output and the string lenght changes when I change the baudRate on Termite and puTTY.
            Heading to work now, I will try AT/r when I arrive there and posts the results here. Thanks.

          2. Is your module working properly apart from having problems in to AT commands responses?

        1. I let it on for like 5 mins, cant feel no temperature change. The power leds is not going completely off, goes down softly, almost a blink.
          Maybe a power problem?

          1. Can you make a video showing the board with power ON for around 2 minutes. Let me see what your network led and status led is doing…

  5. hai sir.why my at commands did not give any responds after i send ‘AT’ at the serial monitor?.when i getting the ‘ENTER’ button,the AT words dissapear directly. the coding that i used was successfull for the first time. then,when i try again, it become the problem that i told just now. the coding still success but the respond did not success

          1. This is my coding sir…but the AT command did not give any respond. so,what should i do sir?i have been sent the video through your an email just now.

            SoftwareSerial GPRS(7,8);
            unsigned char buffer[64];
            int count=0;
            int ledPin = 13;                // choose the pin for the LED
            int inputPin = 2;               // choose the input pin (for PIR sensor)
            int pirState = LOW;             // we start, assuming no motion detected
            int val = 0;                    // variable for reading the pin status
            int pinSpeaker = 10;           //Set up a speaker on a PWM pin (digital 9, 10, or 11)
            void setup() {
              pinMode(ledPin, OUTPUT);      // declare LED as output
              pinMode(inputPin, INPUT);     // declare sensor as input
              pinMode(pinSpeaker, OUTPUT);
            void loop(){
              val = digitalRead(inputPin);  // read input value
              if (val == HIGH) {            // check if the input is HIGH
                digitalWrite(ledPin, HIGH);  // turn LED ON
                playTone(300, 160);
                if (pirState == LOW) {
                  // we have just turned on
                  Serial.println("Motion detected!");
                  // We only want to print on the output change, not state
                  pirState = HIGH;
              } else {
                  digitalWrite(ledPin, LOW); // turn LED OFF
                  playTone(0, 0);
                  if (pirState == HIGH){
                  // we have just turned of
                  Serial.println("Motion ended!");
                  // We only want to print on the output change, not state
                  pirState = LOW;
            void clearBufferArray();
                byte b =;
                if(b == '*')
                GPRS.write( 0x1a );
            // duration in mSecs, frequency in hertz
            void playTone(long duration, int freq) {
                duration *= 1000;
                int period = (1.0 / freq) * 1000000;
                long elapsed_time = 0;
                while (elapsed_time < duration) {
                    delayMicroseconds(period / 2);
                    digitalWrite(pinSpeaker, LOW);
                    delayMicroseconds(period / 2);
                    elapsed_time += (period);
             void clearBufferArray();
              for (int i=0; i<count;i++)
  6. Hello, when i send AT commands to ATWIN Quad-band GPRS/GSM Shield for Arduino using Arduino i didn’t get any response.
    Can you help me please ??

  7. Hi. Can i ask, what could be the problem of the gsm modem if it doesn’t respond to any AT command? Its lights are working though. I’m using sim 900A.

      1. how can i verify this? i read a tutorial where in the AT commands should work on the serial monitor using the default program. Is this true or should all commands be sent through the program itself?

        1. AT commands would work on any baud rate if the modem is in auto-baud mode. Otherwise you need to use the specific baud rate set. In auto-baud mode which is the default settings, you need to AT\r first. All your commands should end with \r. You can use termite to send commands. In settings check end with <cr><lf>

  8. Hello Muhammad Sir,
    I’m using SIM 900A module for making call to my cell phone . The sim card which I had inserted in my module receive’s the call but it does not make call to the provided number.Here’s my code :

    char phone_no[]="xxxxxxxxxx";
     void setup()
     void loop()

    Serial Monitor screen :


    I’m communicating to GSM module via Tx and Rx pins of arduino
    Please provide me the solution for making calls

      1. Dear when you send a command to the modem, there must be some replies from the module. Without knowing that we Can’t know what is the issue. You can connect the module to your PC via serial port and send and receive commands manually.

        1. Sir the Network LED on the GSM module blinks after the program is uploaded and it receive’s the call also but it is not making any call
          I have tried sms chatting with the module using Software Serial Library . At very first time it receives the sms sent to the module and same sms is displayed on the Serial monitor but it is not sending any sms to the registered no.

          1. Dear when you send any command to sim900 it will reply back with response. I would suggest to read more about the basics… Anyhow can you share your complete code…

          2. Sir when I send any commands to GSM , it does not reply practically(eg. When I send ATDxxxxxxxxxx command to gsm then it should call back on the registered no. but it is not making any call .) but actually the serial monitor of arduino shows all the commands send to the gsm module .
            My complete code is same as I shared above .

          3. If our doesn’t t reply or is not getting the commands. There might be a problem in connection or baud rate or your program

          4. Sir I’m using Tx and Rx pins for communication and the baud rate is kept same(9600) but still it is not making any call
            I have used the SoftwareSerial library of arduino for communicating but for this code ths GSM module receives the sms sent to the no. and the sms is displayed on monitor but it is not sending any sms to the registered no.

    1. Dear this is not the way to operate A GSM Module. You would need to send command , check the response and see if the module is ready to make calls or not. My suggestion is go through some nice getting started tutorials. Also go ahead step by step.

      Make sure that your communication is OK.
      Send a command wait for reply. If you are not getting replies check your connection and your baud rate and other settings.

      You have to put effort in the correct direction. If you are using a shield might be helpful

      1. Hi please help me. I have a Sim900a module and facing similar issues as avove. It is getting connected to the network but when I try to call using it ,it doesn’t work. It doesn’t respond to AT commands. I have kept the baud rate as 9600 both in the code and serial monitor. I have connected Rx tx pin of arduino to tx Rx pin respectively. Please guide me.

          1. No sir it still does not work. The arduino and gsm module are not connecting properly I think as their is a baud rate difference between Sim900a and arduino as sim900a is in auto baudrate initially. The gsm module is not bad according to me as I am able to call it and an alarm rings. But it is not able to call other phones. I think the main issue is with the baud rate. When I type AT in the serial monitor and click send it just vanishes and does not come. Please help me.

            I am using this code-

            char phone_no[]=”9953648754″;
            void setup()
            Serial.println(“AT”); // Wake up GSM
            Serial.print(“ATD”); //Dial the phone number using ATD command
            Serial.println(“;”); // Semicolon is a must at the end
            //Open Serial Connection at baudrate 9600
            // After a delay of 5 secs Hang the call
            void loop()

            // empty loop.If you enter the above code here,the call will be made FOR EVER repeatedly.
            //Take Caution while coding under loop.At some condition you’ve to terminate the Call

            It gives me output in the serial monitor-

            No ok is there.

  9. Hi, I am using SIM900A module and it was working fine yesterday (calling, message, http request). Today, nothing seem to work. I am calling the sim card and it is ringing, but not responding to any AT command. Following is the code:

    SoftwareSerial mySerial(9, 10); // RX, TX
    void setup()
      mySerial.begin(9600);   // set the data rate for the SoftwareSerial port
      Serial.println("Calling through GSM Modem");
      mySerial.println("ATDxxxxxxxxxx;"); //I put my number here.
      Serial.println("Called ATDxxxxxxxxxx");
      // print response over serial port
      mySerial.print("AT+CMGF=1\r");    //Because we want to send the SMS in text mode
      mySerial.println("AT + CMGS = \"+91xxxxxxxxxx\"");//send sms message, be careful need to add a country code before the cellphone number
      mySerial.println("A test message from SIM900A!");//the content of the message
      mySerial.println((char)26);//the ASCII code of the ctrl+z is 26
    void loop() // run over and over
    void ShowSerialData()

    Also, I have one A6 module, it works well.

    1. Hi, did you update the firmware? if so you need to let the module know what baud-rate you are using by sending AT a few times. Otherwise there might issues in you communication either wiring or settings

  10. hello muhammad,
    I upgarded my SIm900A with this firmware with this version 1137B03SIM900A64_ST_ENHANCE…,
    Now my SIM900a is not responding to any AT commands , Not even sim card also not working, i call the number it saying not reachable…. Can you tell me where i have done anything wrong …

    1. There could be several reasons. May be the flashing process was not successful or the variant of firmware you used is not compatible…

      Do you know what was the last firmware version?

  11. what does a solid netlight that never blinks indicate? I called provider.. the sim is not lock.. imei is registered to it.. and all is ok on their end.. but the netlight just stays on as solid as the power light.

    1. Does the modem respond to nay AT commands? Does it get hot? There is a chance that the modem might have been damaged and cannot switch on.

      1. It doesn’t get hot at all. The unit came sealed and with an inspection id (it could have been damaged in shipping i guess) but it was well packaged. What is the netstatus behavior if it cannot find the provider? I assume it will still be blinking while trying.. but I’m not sure.

        1. That seems to be a damaged modem. I my self had quite a number of such cases. These modules are too fragile and are easily damaged by reverse polarity or higher voltages.

          1. Ok your comments on power helped. The specs say 5.0 at 450ma… lots of guides online say use a 5v 1a wall wart.. other says 2amp. I didn’t have a 2amp wall wart but I assumed the darn light would blink even if it didnt have enough power for communication.

            I connected to the super charger port on my work machine (2.1amp) and the light blinks! I didn’t see mentioned anywhere online that netlight would remain solid when under powered.

            Problem now is my work machine has UAC and I can’t control the serial ports to try AT commands. I’ll move onto trying some more power supplies. You helped even if you didn’t know it. Thanks.

          2. The net light would be still if the modem doesn’t switch on. Whether it be due to undervoltage overvoltage or of the modem is damaged

  12. Hi Sir, I am using SIM900A GSM module
    Can you tell me how it will be set to AUTOBAUD RATE after I once set the baud rate to 9600

  13. Hi, i have a problem with SIM900 S2-1040S-Z1K18… i had simulate Serial port by arduino and with 19200 of baudrate when i switch on the SIM900 i get right answer:

    +CFUN: 1


    Call Ready

    *PSUTTZ: 2016, 10, 2, 8, 39, 3, “+8”, 1

    DST: 1

    But if i try to send an AT command i don’t get an aswer, or a feedback that the command was sent. i tried with different power, by arduino or external source, change pin… i don’t know the reason, maybe to high bauderate? but ii can change it if the modem doesn’t receive my commands? it could be possibile that serial pin rx is burned, by a change rx tx?

      1. I haven’t but this is the shield

  14. Hi Sir,
    I am using Sim900A.. handling http at commands using user guide..Even AT+HTTPACTION command replied +HTTPACTION: 0, 200 ,10when server is ok.Some time 601 or 604 error came.but server and data package all are ok.when this error came, reset the at commands(ATZ) and also http process going on.but that error repeatedly..after reset(power off and on) the module only working. any idea about without reset the module.

    1. 600 series codes are custom implementation. Check the server documentation or try another server with simple commands to test

  15. I am facing an issues my sim808 was working fine, but after few days it stop responding AT command, it do send a text message on my cell but not responding my AT command i need to send data our GPRS will you please guide me how i can troubleshoot it.

    1. if it sends SMS that means the AT commands are accepted. May be there is issue in your serial port setup or reading from serial port…

  16. hi sir thank u very much for your respond.
    my device info, we are connected gsm900a rx to aurduino rx and gsm900a tx to arduino uno tx, and connected gsm ground to aurduino uno ground.
    i supplyed 12v adapter power to gsm module, and arduino uno connected to my laptop with usb.

    iam calling to gsm module its ringing ,but does not responds my at commands on serial monitor of aurduino studio.
    my commands

    ofter typing AT command, doesnot showing any data on my serial monitor,
    also iam trying different commands


    also iam trying below on ofter changing myconnections,
    rx to tx and tx to rx of aurduino uno and gsm and ground to ground
    arduino uno code

    void setup()
        void loop()
        bool bOK = false;
        while (Serial.available() > 0)
        char inChar = (char);
        bOK = true;
        Serial.println("AT+CMGF=1"); // sets the SMS mode to text
        bool bOK = false;
        while (Serial.available() > 0) {
        char inChar = (char);
        bOK = true;
        Serial.print("AT+CMGS=\""); // send the SMS number
        Serial.print("hi  this is test from aurduino ."); // SMS body

    pls give me the proper sollution for this.
    thank u

      1. i tried that one rx to tx and tx to rx but not working and my board buy on below link

        any problem in this bhoard its working or not

        its replies on serial board following code from arduino board to arduino studio serial monitor as following



        repeatedly comming this one

        1. Try to connect the Rx of sim900A to Tx of your PC. don’t confuse it with Rx , Tx of the DB9. Most probably the pin2 of DB9 connector will be connected to Tx of Sim900A … track with a multimeter please

  17. hi have using sim900a for aurduino uno r3 the bhoard is working but not responding AT COMMANDS FOR
    message send and reciving purpus pls give me the sollution for that and reasion

    1. does it reply to other AT commands?

      Please share the log of the commands you send and the replies and the initialization commands you use to setup the modem.

      Most probably it might be because the modem is set to PDU mode for SMS but I can’t be sure of that until you provide more details. Did you use AT+CMGF=1 command?

  18. Hello sir, I am using SIM808 module from I have inserted SIM properly and given required power from the adapter and also connected with USB, It shows me “Silicon Labs CP210x USBx to UART Bridge (COM2)” in device manager in computer. But when I give AT command it does not reply me anything. I can make a call to SIM and can hear tone, but It does not respond to AT commands. Please help me out

    1. you need to setup the serial port correctly. Rx->Tx and Tx->Rx. Furthermore you have to send AT\r so that the modem knows what baud rate your are trying to communicate. Once you receive back OK you can fix the baud rate by using AT+IPR=x command

  19. my gsm module is not working with putty terminal as i have used 12 v and 1 ampere supply . I am getting the phone call over it but its not responding to AT commands . plzz help me out with this.

  20. Hey there i have a SIM808 (with GPS GPRS and Bluetooth) which is not talking at all. How can I reflash the firmware?

      1. Were you able to communicate before?

      Most probably there wont be problems with firmware. There can be issues with baud rate settings or communication setup!

      1. no i wasn’t able to communicate. i tested different baudrates and the module should be still on self adjusting mode.

        the strange thing is, i only got one a ÿ character back and now never again.

        the module seems also to be running but i can’t get a connection

        1. When you realize that ÿ character, you should send back AT followed by carriage return as described in the post. Make sure AT IS IN CAPS

  21. I am using SIM900A talky version. It has no reset pin on board. It was working fine until now but suddenly after powering it on, its getting hot and a red light is constantly glowing with continuous beep sound. no matter how many times i switch it on or off but still it doesnot accepts any AT commands. what to do now?
    where is the reset pin? can you atleast tell me the reset pin number in sim900A chip?

    1. when the modem is getting hot that is a sign of a damaged modem… I have several of them …. sadly “its dead”.

  22. Good day,
    I got simcom sim800L and make all connections, run a simple test example of AT commands its Okay, now try to call or sent sms is not going while the AT command shows ready for call and sms. my gsm carriers are MTN nigeria and Airtel Nigeria.
    I need a helping hand i think of updating the firmware?

    1. You must be having some other problem and that you have to fix instead of doing a firmware upgrade. I can’t help unless you provide your code or commands and their responses .

  23. Hi ,
    Iam facing problems with sim900 module.
    Iam not getting any response from it.
    I tried calling to the sim card which is inserted into it.But not receiving any ringing tone.

      1. Hi, i am also facing the same problem where i do not get a response from the module and yes the module is power up correctly. I have also tried sending AT command and i am getting symbols as replies.

        1. symbols as response !! Can you share a screenshot? seems to be problem elated to baud rate mismatch… Please provide the following dettails

        2. baudrate
        3. exact symbols you get
          1. ÿ ÿ ÿ shows that the modem is in auto baud rate mode. You should send AT\r a number of times until you get OK from the modem. (DO NOT FORGET TO SEND THE COMMAND AT IN CAPS).

          2. Hi, I have tried you suggestion of sending AT\r commands to the modem but i am getting the same response and sometimes no response at all. If it helps i think the problem with my modem is the baud rate because it was working fine until i change the baud rate through arduino coding and i do not know how to change the baud rate back. Is there a way to change the baud rate back or reset the whole modem?

  24. Hi,

    I am interfacing sim900a to kinetis controller vi rs232. The controller sends at command to gsm modem ,but doesn not receive anything from gsm modem..I tried connecting gsm modem to pc and it works fine.also ,the controller is also able to send and receive data. Kindly let me know what could be the issue

  25. Hi. Thank you for replying to my post, my query is will sim900A_revisoion 1137B14SIM900A32_ST work for HTTP commands… bcoz when i issue the HTTP commands it is returning is happening in all of the SIM900A modems with the same firmwar

  26. Hi.

    Thank you for replying to my post, my query is will sim900A_revisoion 1137B14SIM900A32_ST work for HTTP commands…
    bcoz when i issue the HTTP commands it is returning is happening in all of the SIM900A modems with the same firmware

  27. Hi,

    Very glad of you providing information about SIM900 modems.I was just struck with upgrading a SIM900A series gsm modem to SIM 900 modem

    Firstly, the revision read by SIM900A modem reads as follows


    As i was unaware of this revision,
    I loaded the firmware of SIM 900 which is named as follows

    1137B09SIM900M64 normal_ST

    Since then the modem stops responding,at all the baud rates I’ve tried..

    I suspect the revison above is 32 and below i flashed is of can i get it back to normal state..

    And In this SIM900A_32 revison the HTTP commands are giving errors,pls help me out ..

    Thank you

    1. Hi, i have the same issue. my firmware is same as yours and get Error for HTTP. But it not working yet, means get error for every http commands. how can i fix it? tried reset it but it not working

  28. SIM900A stop responding after hours of standby is there any way to reset it by commands when it hangs
    i am sending hourly data to FTP server but after 3 to 4 hours it stops reponding i have to restart my controller and gsm both i have cheked controller is working it have two uart one is responding other is tied to gsm sim900a

    please sir let me know is there any way to reset by commands

  29. HI i Have updated SIM900A with i am getting continues blinking of network status led with garbage data on TX after updateting firmware (64bit older was 32) i have tried all available baud rate to get what exectly transmitting from modem but i am getting only YYYYYYY

    1. You need to match the 64M and 32M softwares as they represent the amount of memory and often wont work interchangeably. From your case it seems it worked.

      Your modem is now in autobaud mode. So switch off modem-> switch on –> send “AT\r” command a few times. It will recognize your baud rate

  30. Hi i have sim900a module. it has tx rx g 5v pins. i connected them with arduino using software serial.
    pins 10,11. i am able to send AT commands. call sms everything works.
    but i dont get any response for any of the commands.
    is it possible that the tx of gsm board is not working?

  31. Hi,
    I have to communicate a HMI with a GSM modem. I tried communicating using hyper terminal from PC and I get perfect replies from the modem. However, when I send commands from HMI to the modem,I receive the same given input command in the output as well.
    Request to please help.

  32. I ‘am also trying to flash SIM900A, mine one got folowing release

    And doesn’t work here in Italy. Module does not connect to the GSM net.

    All the flashing tool report now this error:
    00’00 “000 – 24/12/2015 19:49:02
    00’00 “000 – Opened COMM port
    00’00 “000 – Power On / Reset Target
    00’04 “672 – Sending RAM program
    00’06 “375 – RAM program send completed
    00’06 “391 – RAM program loaded.
    00’06 “391 – Waiting for ACK RAM program.
    **00’06 “391 – ERROR RAM program ACK Not received! (0)***

    what does it depends on? i’m stuck

      1. Thanks. Actually I kept down “NRESET” pin while clicking on “start download”, then i release pin 16, and download starts. Ok it works! But I couldn’t find a firmware working. All those I tried don’t work. System reports “Error The type of FLASH Does not match the firmware…”. It will likely depends on the fact that flash size is only 32Mb… any suggestion?

  33. i have sim900a modem and i made a shield of it . during using it suddenly my vbat and ground giving connectivity and modem went hot . now its continuously giving VBAT and Ground Connectivity is that means my modem damaged ?

    AND UNFORTUNATELY THE PROGRAM “Simcom – Customer sim900 flash loader V1.01.exe” DOES NOT GENERATE AN ERROR

    err 00 update option does not support this Flash
    Err 00 Error during get mindful device

    I tried using the program download Tools SIM900 Series Customer 1.8.exe

    00'00 "000 - 24/12/2015 19:49:02
    00'00 "000 - Opened COMM port
    00'00 "000 - Power On / Reset Target
    00'04 "672 - Sending RAM program
    00'06 "375 - RAM program send completed
    00'06 "391 - RAM program loaded.
    00'06 "391 - Waiting for ACK RAM program.
    00'06 "391 - RAM program ACK received.
    00'06 "500 - Flash Man ID: 0x01
    00'06 "500 - Dev Flash ID: 0x007E
    00'06 "500 - Flash Ext ID1: 0x0063
    00'06 "500 - Flash Ext ID2: 0x0001
    00'06 "500 - Flash Name:
    00'06 "500 - Manufacturer: Spansion
    00'06 "500 - Flash Size: 128 Mb
    00'06 "516 - ERROR The cla file does not match the Target List! (0) ------
    00'23 "922 - 24/12/2015 19:49:26

    AT +

    1. Hi,

      you have a Sim900A with Spansion memory chip. you should use firmware that is for this variant! As you already erased the Flash you need now to atleast flash with the previous version you had. Check this post for firmware with Spansion tag in the name .

  35. I having one problem with 900.Max 232 becomes hot and also the LM317 (onboard) when i connected to supply.Power and network status are i changed the Max 232 smd ic.Now the lm317 and max 232 becomes normal,but i can’t communicate with pc.But Network registration is done.

  36. Hello Muhammad.

    I need your help please, I bought a sim908 without board only the module, I designeda little board to connect this to the breadboard, at this moment the nethligh is flassing at 800 ms off, but the probel is AT commands, I mean, when turn on the module I send “AT” command, but the mdule response with the same command, I tried with “AAAAT” “A” or “ATr” but nothing happen, Ihave read the manual and say:
    “”DTR shall be pulled up to invalid state at least 2 seconds by DTE”, do you know what should Ido?

    Thanks in advance.

    1. do you mean you get an echo of what you send?

      send AT and you get back AT ?
      send ATD and you get ATD back?

      1. Hello i am using SIM800 mounted on board module and i am having this issue, when i send AT from serial terminal i receive AT, any AT command which i am transmitting is echoing back to me, no command is having any effect.
        Also when i call on GSM module it sends “.RING.” to serial terminal also when i am sending msg to module i am also getting notified in some format which is correct according to datasheet.
        I can not find a way to make my at commands effecting please suggest something.
        Thanks in advance.

          1. Actually there was some issue with my terminal software now i am using putty and it is working fine…please suggest some good terminal software.
            thank you soo much for your responses.

  37. Hi
    I’ve tried flashing the SIM900A with a variety of different 64bit firmware versions (for both sim900 and sim900a).
    the flash completes successfully (as reported by the tool). I’m using an arduino nano as a USB-Serial controller (disabling the 328p chip by shorting RST to GND).
    In every case, without fail, after flashing the module (3.8.2 mini) remains in bootloader mode after rebooting – with both power and netlight flashing rapidly and continuously.
    Do you have any experience of breaking out of this loop? or is there perhaps a step in the flashing process that the loader does not intermediate?


    1. module (3.8.2 mini)

      What is that?

      with both power and netlight flashing rapidly and continuously.

      I havent experienced or came through any such situation . I’ll recommend to contact simcom support.

      1. thanks Dost. the board is just a break out module. cheap from china. with a max232 level shifter so that i can take 5v and 3.3v TTL i/o.

        i contacted sitcom support a few days before trying this board! no answer at all ;-(

          1. Hi, what are the labels with those leds?

            Can you check if your sim900A gets HOT??

          2. the chip doesn’t get hot, no. I’ve tried feeding it with different voltages between 4 and 6v but not change in temperature.

            the silk screen for both LEDs just references a diode (Dn). however the LED at the edge of the board connects to pin 52 (netlight) and to a via that is labelled “status”. which is annoying as there is no connection to pin 66.

            the LED in the middle of the board is connected to pin 4 (RI).

            both have resistors in series. difficult to get my probe on them but I’d guess they are 1kΩ.

          3. Applying power more than 4 volts is ging to damage the pin. I have no idea why the RI LED should blink like that……. 🙁

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