How to Transmit Raw Decimal Values (0-255) using UART?

[AsifShaik]

Hi I would like to ask if there is any possible alternative to how I'm transmitting values from my STM32F407 Discovery to my PC which receives and buffers the data using a Python program. 

These are the functions I'm using to transmit my values:

void Serial_logi(int val) {
	char buffer[10];
	itoa(val, buffer, 10);
	Serial_log(&buffer[0]);
}

void Serial_log(char *s) {
	while (*s) {
		while (USART_GetFlagStatus(USART2, USART_FLAG_TXE) == RESET)
			; // Wait for Empty

		USART_SendData(USART2, *s++); // Send Char
	}
}

The current implementation converts the decimal value which I wish to transmit, val (0-255) into a string of characters, and then transmits the string character by character. 

The problem with this implementation is that when I use my Python program to receive the data it does not store it as I want. For example, when I transmit the value 255, instead of storing the first byte as 255, it stores 50 as the first byte because the ASCII value of 2 is 50, and the remaining 2 bytes as 53 each which is the ASCII of 5. The python snippet I use to store and print the values is shown below:

    ReadData = sport.read(3)              
    startbyte = ReadData[0]
    nDisLineNo = ReadData[1] 
    numbyte = ReadData[2]
    print(startbyte)
    print(nDisLineNo)
    print(numbyte)

All in all, I will be using the transmission code to transmit 3 identifiers(ranging from 0-255), followed by pixel values that range from 0-127. I would like to ask if there is any way to modify my functions such that I can transmit raw decimal values ranging from 0-255, such that when I read them on my Python program, it is able to distinguish between each byte that I transmit. Thanks!

I've attached a sample of what my data looks like in the serial monitor below. The first three bytes are identifiers I use to indicate the start of the line, line number, and number of pixels in one line (255,3,176), while the rest are pixel data. 

[Andrew Neil · Accepted solution]

The UART just transmits bytes - so, yes you can transmit any value from 0-255.

But, when you do that, you will not get human-readable text - it will just be the pure binary byte values.

Therefore the thing which receives it (your Python code) must be expecting pure binary - not text.

[Tesla DeLorean]

For ASCII, probably want to send a separating character like a space or comma

To send bytes

uint8_t data[] = { 255, 3, 176 };

void UARTSendBinaryData(uint8_t *buffer, int size)
{
  while(size--)
  {
     while (USART_GetFlagStatus(USART2, USART_FLAG_TXE) == RESET)
       ; // Wait for Empty

     USART_SendData(USART2, *buffer++); // Send Byte
  }
}

UARTSendBinaryData(data, sizeof(data));

[AsifShaik]

Thank you so much for this, all this while I was trying to transmitting decimals, I was doing it correctly but assumed it was incorrect because I could not see it using a serial monitor. I only now realized that raw decimals transmitted via UART will come up as gibberish in the terminal, but when I read and display them using Python it verifies that my transmission is accurate.

[Andrew Neil]

---

@AsifShaik wrote:

 I was trying to transmitting decimals

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Remember, the UART just transmits bytes - whether you choose to visualise the content of those bytes as decimal, or hex, or binary, or ASCII, or anything else is entirely irrelevant to the UART.

[Tesla DeLorean]

Things like RealTerm can show you hex codes