Sendind Strings to a device following a protocol

[acjacques]

Dear friends;

I need to send several strings to a device. But in order to work the device requires that I send according a protocol. For example to send the string "hello" at position X =5 and Y =12 i will need send: (Serial.write)

3 fixed bytes (commands to write )
1 byte (position X variable = 0x05)
1 byte (position Y variable = 0x0C)
10 bytes : (0xA3) , ("h"), (0xA3,("e"),(0xA3), ("l"),(0xA3),("l"),(0xA3),("o") (need to add 0xA3 (fixed) before each character of the string)
1 byte (chksum) chksum = exor of all above bytes

What is the best way to do this ?
I mind something like:

x= 5;
y=12;
mystring = "hello";

callMyFunction();

void callMyFuncion {
????? how implement this function ?
}

[JohnRob]

I needed to send data (in bytes). The actual output is in string format, i.e. 45.3 is "4" "5" "." "3"
So I created an array of bytes. Filled in the locations I needed to and set it out using the UART.

void sendHubitat(){
	zArray[0] = mHumidity;
	zArray[1] = round(mTemperature);					// units)
	zArray[2] = round((mTemperature - zArray[1])*10);	// tenths
	//zArray[3] = ETX  pre declaired global.
	Serial.write(zArray,sizeof(zArray));
}

[sherzaad]

something like this maybe:

void writeText(uint8_t x, uint8_t y, char *str) {
  int i = 0;
  uint8_t checksum = 0;
  
  //send write command
  Serial.write(writecommandbyte1); //update with the ACTUAL byte value!
  checksum ^= writecommandbyte1; //update checksum
  Serial.write(writecommandbyte2); //update with the ACTUAL byte value!
  checksum ^= writecommandbyte2; //update checksum
  Serial.write(writecommandbyte2); //update with the ACTUAL byte value!
  checksum ^= writecommandbyte1; //update checksum

  //send 'x' value
  Serial.write(x);
  checksum ^= x; //update checksum

  //send 'y' value
  Serial.write(y);
  checksum ^= y; //update checksum

  //send string
  while (str[i] != '\0') {
    Serial.write(0xA3);
    checksum ^= 0xA3; //update checksum
    Serial.write(str[i]);
    checksum ^= str[i]; //update checksum
    ++i;
  }

  //send checksum
  Serial.write(checksum);
}

void setup() {
  uint8_t x = 5;
  uint8_t y = 12;
  char str[] = "hello";

  Serial.begin(9600); //update baudrate to match device speed

  writeText(x, y, str);
}

void loop()
{

}

note that you did not provide the write command byte so I could not include in it this sample code. please update accordingly.

Hope that helps....

[gcjr]

consider

dispBuf
 01 02 03 05 0c a3 68 a3 65 a3 6c a3 6c a3 6f c8

#define BUF_SIZE  80
byte buf [BUF_SIZE];

byte prefix [] = { 1, 2, 3 };

// -----------------------------------------------------------------------------
int
msg1 (
    byte       *buf,
    int         maxByte,
    byte       *prefix,
    byte        x,
    byte        y,
    const char *s )
{
    if (BUF_SIZE < strlen(s) + 6)
        return -1;

    memcpy (buf, prefix, 3);;
    buf [3] = x;
    buf [4] = y;

    int n = 5;
    for (unsigned i = 0; i < strlen(s); i++)  {
        buf [n++] = 0xA3;
        buf [n++] = s [i];
    }

    byte chksm = 0;
    for (int i = 0; i < n; i++)
        chksm ^= buf [i];
    buf [n++] = chksm;

    return n;
}

// -----------------------------------------------------------------------------
void
dispBuf (
    byte *buf,
    int   nByte )
{
    char s [80];
    Serial.println (__func__);
    for (int i = 0; i < nByte; i++)  {
        sprintf (s, " %02x", buf [i]);
        Serial.print (s);
    }
    Serial.println ();
}

// -----------------------------------------------------------------------------
void setup (void)
{
    Serial.begin (9600);

    int n = msg1 (buf, BUF_SIZE, prefix, 0x5, 0xC, "hello");
    dispBuf (buf, n);
}

// -----------------------------------------------------------------------------
void loop (void)
{
}

what you describe is the format of a message, not a protocol

a protocol is the sequences of messages between two (or more) endpoints allowing them to reliably exchange a set of commands or data