Sending CTRL-Z over UART

[frijj2k]

Hi, I have a SIM800L GSM/GPRS module that I can successfully talk to via the UART on the nRF51.

I can tell it to dial numbers etc and that all works fine.

My problem is that to send an SMS, the final character (after inputting the message) needs to be a CTRL-Z sequence. (Dec 26 - Hex 1A)

If I enter the AT commands via a terminal and an FTDI cable, everything is working. But when I try sending the sequence from the nRF51's UART, everything 'looks' good apart from the CTRL-Z character which shows itself as a '.' on my terminal and the SIM800L module ignores it.

I have tried placing the CTRL-Z sequence within my string via sprintf and also I have tried manually sending it at the very end directly via app_uart_put as follows...

err_code = app_uart_put((uint8_t)0x1A);  // CTRL-Z

But this doesn't work.

What am I doing wrong?

Thanks in advance!

[frijj2k]

Some more information (code)...

#define CTRL_Z 26

void uart_putstring(const uint8_t * str) {
    uint32_t err_code
    uint8_t len = strlen((char *) str);
    for (uint8_t i = 0; i < len; i++) {
        err_code = app_uart_put(str[i]);
        APP_ERROR_CHECK(err_code);
    }
}

void dial_number(const uint8_t * number) {
    char cmd_string[255];
    cmd_string[0] = '\0';
    sprintf(cmd_string, "ATD%s;\r", number);    
    uart_putstring((uint8_t*)cmd_string);
}

void send_sms(const uint8_t * number, const uint8_t * message) {
    uint32_t err_code;
    char cmd_string[255];
    char msg_string[255];
    cmd_string[0] = '\0';
    msg_string[0] = '\0';
    
    //sprintf(cmd_string, "AT+CMGS=\"%s\"\r%s\032\r", number, message);   // \032 = CTRL-Z
    //sprintf(cmd_string, "AT+CMGS=\"%s\"\r%s%c", number, message, CTRL_Z);
    //sprintf(cmd_string, "AT+CMGS=\"%s\"\r%s", number, message);
    
    sprintf(cmd_string, "AT+CMGS=\"%s\"\r", number);
    sprintf(msg_string, "%s", message);
    
    uart_putstring((uint8_t*)"AT+CMGF=1\r");    // Set TEXT mode cmd
    uart_putstring((uint8_t*)cmd_string);       // Send to number cmd
    uart_putstring((uint8_t*)msg_string);       // Send actual message
    err_code = app_uart_put((uint8_t)0x1A);     // Send CTRL-Z to finish	    
    APP_ERROR_CHECK(err_code);
}

// USAGE...
dial_number((uint8_t *)"07123456789");	// This works!
send_sms((uint8_t *)"[phone]", (uint8_t *)"This is a test message from SIM800L");	// This sends all commands but final CTRL-Z isn't received correctly by modem

Please note, the original code only had cmd_string (no msg_string) but I split it up and added fixed delays to see if timing was a problem but that had no effect either...

Hopefully somebody can shed some light on this... (As you can see... I have tried many ways to send that CTRL-Z, all of which have not worked) Thanks!