11 months ago.  This question has been closed. Reason: Off Topic

A two way serial communication

Hi, I've created a simple two way serial to get AT commands from pc and send them back to a Quectel GSM modem. First I tried to use standard serial from mbed but somehow it stuck (or maybe overflowed) after receiving data from the modem. I used BufferedSerial library https://os.mbed.com/users/sam_grove/code/BufferedSerial which works fine but it lacks some functions like `scanf` or `gets` so I need to read chars by using `getc` function.

#include "mbed.h"
#include "BufferedSerial.h"

DigitalOut modem_pwr(PD_3);
DigitalOut modem_sw(PB_12);

Serial pc(PA_9, PA_10); // tx, rx
BufferedSerial modem(PC_6, PC_7);

void strInput(char str[], int nchars)
    int i = 0;
    int ch;
    while ((ch = modem.getc()) != '\n' && ch != EOF)
        if (i < nchars)
            str[i++] = ch;
    str[i] = '\0';

void two_way_serial()
    char temp[200];
    if (pc.readable())
        pc.scanf("%[^\n]", temp);
        if (modem.writeable())
            modem.printf("%s\r\n", temp);
            memset(temp, 0, sizeof(temp));
    while (modem.readable())
        strInput(temp, sizeof(temp) - 1);
        pc.printf("%s\n", temp);
        memset(temp, 0, sizeof(temp));

int main()
    relay = 1;
    modem_pwr = 1;
    modem_sw = 1;
    modem_sw = 0;
    pc.printf("Setup Complete!\n");
    while (1)

I have two problems with this code: 1. when I send a command I receive my answer plus all previous commands and answers. 2. after sending some commands I get a huge amount of previous data in the terminal which is strange for me. I'm using an STM32F407 board and using Serial6 pins.

3 Answers

11 months ago.


Thank you, but I still have the problem. It seems that my data is not sent to the modem. I can see the incoming data.

posted by Masoud R. 29 Nov 2018
9 months ago.

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Thanks, I solved it by using mbed's UARTSerial API.

posted by Masoud R. 15 Jan 2019
10 months, 2 weeks ago.

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