Almost there, need Assistance ! MCU to Hyper Terminal OK. GSM Modem to Hyper Terminal OK. GSM TO MCU = Garbage

[Chen Jun Jie]

Hello everyone,

 

I’m about to solve my problem.

 

MCU to Hyper Terminal, sends ABC, receives ABC.

 

GSM Modem to Hyper Terminal OK.

Able to send sms.

 

 

However, Gsm to MCU, i get errors. I pick up garbage data instead.

Baudrate is set to 115200.

I am using the following setup.

 

GSM MODEM TO Hyper Terminal Setup

RX of GSM  -> PIN 5 of MAX233 (T1out)

TX of GSM -> Pin 4 of MAX 233 (R1in)

 

PC Serial

SerialTX to Pin 2 Max233 (T1in)

SerialRX to Pin 3 Max233 (R1out)

 

 

I can send Sms no problem.

 

 

MCU to Hyper Terminal

 

MCU Uart3 TX -> Pin 2 of MAX233

MCU Uart3 RX -> Pin 3 of MAX233

 

Serial Pins as per normal

 

I can send random ABCs, and receive ABCs on my MCU

 

 

 

MCU TO GSM MODEM

 

MCU

 

MCU Uart3 TX -> Pin 2 of MAX233

MCU Uart3 RX -> Pin 3 of MAX233

 

GSM Modem

 

RX of GSM  -> PIN 5 of MAX233 (T1out)

TX of GSM -> Pin 4 of MAX 233 (R1in)

 

This is my problem, my mcu is currently sending AT+CMGF=1

I should receive OK,

however, i receive this instead

 

PUi53531u1

AT+CMGFPUi53531u1

Please let me know if you can spot the problem.

 

 

My Code to print out what i have received.

if (LPC_UART3->LSR & UART_LSR_RDR) //To modify, perhaps a better way.

 

   {

       do

       {

        UART_Receive(LPC_UART3, &data, 1, BLOCKING);

        //Timer0_Wait(500);

           if (data != ‘r’)

           {

            len++;

            line[len-1] = data;

           }

       } while ((len<64) && (data != ‘r’));

   }

 

        line[len]=0;

 

        printf(“%sn”, line);

 

 

 

 

[nikhiljain]

Hello,

 

Please check the GSM interfacing projects and tutorial on this website and your problem will be solved. Pls note the GSM modem also sends some additional characters with the data like “OK”. They are some special characters like line feed, carriage return etc and hence there is garbage data.

 

There is a standard pattern of sending and reciveing data to the modem. When you recieve the data you need to remove/filter/reject/some of the bytes to discard the unwanted data and capture only the data you want. Similar is the case while sending the data to the modem. In sending you have to add the charchters.

 

Please go through the GSM based work on the website in the 8051 section.

[Chen Jun Jie]

Thank you Nik for the reply.

 

Believe me, i have read literally the entire internet resource on this topic.

 

 

But the problem that i am facing is really driving me crazy.

 

 

I see no issues to communicate from GSM modem to Hyper Terminal, or Hyper Terminal To MCU.

 

My code should be working.

 

 

But MCU to GSM Modem, i am not able to receive the “OK” from it.

 

Need help.

[nikhiljain]

Hi,

 

Read the following three article in order:

 

http://www.engineersgarage.com/microcontroller/8051projects/gsm-interface-8051-microcontroller-circuit-code

http://www.engineersgarage.com/microcontroller/8051projects/interface-gsm-module-8051-microcontroller-circuit-code

http://www.engineersgarage.com/microcontroller/8051projects/interfacing-gsm-8051-microcontroller-circuit-code.

 

To me it appears that all you are doing is a logical error in understanding the working of GSM modem.

[nikhiljain]

Hi,

 

Please search the following three project having project code: MC074, MC075 & MC076 in the 8051 section of this website under EG labs. You are misunderstanding the logic behind recieving and sending text to GSM modem.

[Chen Jun Jie]

Dear Nikh,

 

I have seen the 3 projects and in detail.

 

 

 

MAX 232

tx Micro Controller to t1in of max232  pin11

rx MICRO Controller r1out of max232 pin 12

rx modem  t1out of max232 pin 14

tx modem r1in of max232 pin13

 

Now max 233

Micro controller tx to T1in max233 = pin 2

Micro controller rx to R1out max233 = pin 3

Rx of modem to T1out max 233 = pin5

Tx of modem to R1in max 233 = pin 4

 

 

I used a slightly different ttl logic regulator.

This is the only thing, i can think of, that is different from the 3 projects.

 

Can you be alittle clearer if you know where is the problem ?

 

Much thanks

[Chen Jun Jie]

I have solved the issue

 

 

However, i am not sure how do you send Control Z from C code, any help guys ?

 

 

 

      strcpy(msg,”CAN YOU SEE ? SENT FROM MCU”);

        UART_Send(LPC_UART3, (uint8_t *)msg , strlen(msg), BLOCKING); //strlen :Length of Transmit buffer    Checking Blocking.

 

        strcpy(msg, 0x1A);

 

        UART_Send(LPC_UART3, (uint8_t *)msg , strlen(msg), BLOCKING); 

 

 

 

Should i do +char(26) ?

[AJISH ALFRED]

 

Hi Chen,

 

You are right, the ascii value for ctrl+z is 26, but there is a problem,

 

This is the syntax for strcpy

char * strcpy ( char * destination, const char * source );

The arguments are pointers to memory location. If you give an integer value it will point to that location.

 

Try to do it without strcpy.

[midhun]

You can send the hex value of CTRL+Z ie, 0x1A

Try this. you will…

[Chen Jun Jie]

Thank you everyone for the support. I have since completed the entire project.

 

Working properly on an ARM processor

[Pradeep Kumar]

Hi chen,

 

                   I am facing the same problem. I receive PU8 when i transmit  “AT” and PUi5 when i transmit “AT+CMGF=1”. How did you solve this issue.

 

 

 

[Pradeep Kumar]

I got it!!!

I made a mistake in circuit connection. TXin RXout pins from RS232 to gsm modem were interchanged…
Now working fine

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