Problem interfacing gsm module with stm32h747 disco board

[KiruV]

We're working a camera based person fall detection device with STM32H747 and B-CAMS-OMV camera module, we want to interface GSM module with it to make alert calls in case of fall being detected but we're facing issues with the same.

 

We're not able to interface the GSM module properly with the board,

the GSM module is being powered up and getting connected to cellular network but it's not responding to commands from the board. 

 

We're trying to set up USART communication between the board and the GSM module but the GSM module is not responding to the commands.

 

Kindly help us with the same.

 

[Mike_ST]

Hello,

Check baurate/parity/stop bit configuration.

[Andrew Neil]

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@Mike_ST wrote:

Check whether your module expects "\r\n" or just "\n" at the end of each AT command.

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The AT command terminator should be just CR.

[Andrew Neil]

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@KiruV wrote:

We're trying to set up USART communication between the board and the GSM module but the GSM module is not responding to the commands.

---

So what testing/investigation/debugging have you done to find what's going on?

• Is your code actually transmitting anything at all?
• Is your wiring correct & complete - eg, does the module require just TX/RX, or does it also need other lines?
• Is your code transmitting at the correct voltage, with correct baud rate, etc?
• If all the above are correct, is your code actually sending valid commands?
• Are the commands actually reaching the GSM module? 

Before getting into embedded code, have you manually tested your interactions with the GSM module using a terminal?

In the Posting Tips are some hints on debugging serial comms:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/tac-p/706966/highlight/true#M49

Try those to see what's actually happening between your STM32 abd the GSM module...

[KiruV]

First in order to debug, I tried manually testing USART communication separately:
        * I've separately tried USART communication between PC terminal and STM32 board- it works,
        * Separately tried communication between GSM Module and Arduino-it works.
The GND of both the STM32 and GSM has been connected commonly.

the GSM is still not responding to the AT commands, I sent a simple AT command for which the module is supposed to reply with OK but it is not doing so.

 

 

Code:

 

Is there anything I could be doing wrong? What can i try to do now

[KiruV]

I tried another debugging, I connected PD5(which is the USART2 Tx) to PD6(Rx) directly and tried a loopback test just to see if the channel is working.....it is not, the loopback test itself fails..

so i think the mistake is in the configuration and initialization itself,
but I can not tell what is wrong with the configurations, everything seems to be correct.

 

 

 

[liaifat85]

Some GSM modules can echo back sent characters. Try sending simple AT commands like AT\r\n and see if you get an OK response.

[Andrew Neil]

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@liaifat85 wrote:

 Try sending simple AT commands like AT\r\n .

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The command terminator is just CR:

https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=323

https://www.itu.int/rec/T-REC-V.250 (supersedes the https://www.itu.int/rec/T-REC-V.25ter referenced in GSM07.07)

 

 

[Pavel A.]

Try this simple loopback program to test communication between STM32 and the GSM.

It uses two STM32 UARTs, one to the PC (maybe via debugger VCP) another to the GSM.

Assume the UARTs are already set up.

On the PC type commands in some terminal app like teraterm, observe output.

 

 

#include <stm32f7xx_ll_usart.h>

extern UART_HandleTypeDef huart5; // Modem
extern UART_HandleTypeDef huart2; // Terminal

void t_modem_loop()
{
 USART_TypeDef *UW = huart5.Instance;
 USART_TypeDef *UT = huart2.Instance;
 for(;;)
 {
 if (LL_USART_IsActiveFlag_RXNE(UW)) {
	 if (LL_USART_IsActiveFlag_TXE(UT)) {
	 LL_USART_TransmitData8(UT, LL_USART_ReceiveData8(UW));
	 }
 }

 if (LL_USART_IsActiveFlag_RXNE(UT)) {
	 if (LL_USART_IsActiveFlag_TXE(UW)) {
	 // Stop on ^C
	 uint8_t ch = LL_USART_ReceiveData8(UT);
	 if (ch == 3) {
		 break;
	 }
	 if (ch == '\n') {
		 ch = '\r';
	 }
	 while (!LL_USART_IsActiveFlag_TXE(UT)) {}
	 LL_USART_TransmitData8(UT, ch); // echo
	 LL_USART_TransmitData8(UW, ch);
	 }
 }
 }
}