What is parity? How to use C language?

When configuring serial port in serial port tools and code , You often see parity . So what is parity , What is its function ？ Let's listen to the blogger ~

1. Why should there be parity ？

It is a verification method introduced to solve the problem that the received data is inconsistent with the sent data due to environmental interference in the process of data transmission , Its advantage is that it's easy to implement , The disadvantage is that the accuracy of verification is not high , The error detection rate is only 50%, For example, even bits are disturbed and flipped at the same time , Then parity cannot be checked . And can only judge wrong , Data sending error cannot be corrected , Only resend ;

2. What is parity ？

The last bit of the sending end data is increased by parity bit , After converting the data into binary bit1 The number of is odd or even ; Determine at the receiving end bit1 Whether the number of is odd or even , This verifies whether the data is accurate in the transmission process ;
It is divided into odd check and even check ;
Odd check ： After the sent data is converted into binary , Add check bit ,bit1 The number of must be odd . If the data sent is even , Then the last parity bit is added 1, On the contrary, it is odd , Then add 0; The receiver judges that the data is bit1 Whether the number of is odd , If so, the data is valid , Otherwise, the data is invalid ;
Even check ： After the sent data is converted into binary , Add check bit ,bit1 The number of must be even ; If the data sent is even , Then the last parity bit is added 0, On the contrary, it is odd , Then add 1; The receiver judges that the data is bit1 Whether the number of is even , If so, the data is valid , Otherwise, the data is invalid ;
As shown in the following results ：
6666 After converting to binary, it is 1101000001010, among bit1 For the 5, Odd number . therefore , Parity check needs to be filled in its last digit 1; Odd check needs to be filled in its last digit 0;

3. Parity checked C Language implementation ？

Understand the meaning of parity , Then use C Language implementation is also easy , See the following code for details ：

#include <stdio.h>
#include <stdlib.h>

#define uint8_t unsigned char
#define uint16_t unsigned int

/* * PARITY_CHECK_DATA_TYPE:  Type of data bit  * PARITY_CHECK_PACK_TYPE:  The type of packet encapsulated after parity  *  explain ： These two aliases can be used to define data bits of different lengths , Better applicability . *  However, it should be noted that a parity bit should be reserved for data bits （ For example, the type of data bit is unsigned 16 When a , Its data range is  0 ~ 2^15） */
typedef uint16_t  PARITY_CHECK_DATA_TYPE;
typedef uint16_t PARITY_CHECK_PACK_TYPE;

// Binary conversion of integers  
void FuncOutputBin(uint16_t value)
{
    
	char string[17];   // parameter types uint32 The maximum is 16 position , So here I define the size as 17 The string array is used to store 
	itoa(value, string, 2);  
	printf("%s\r\n",string);
}

/* * value:  Data to be sent  * mode : 1 Indicates odd parity ,0 Indicates even parity  *  Return value ： Use parity to encapsulate the data  */ 
PARITY_CHECK_PACK_TYPE ParityCheckSend(PARITY_CHECK_DATA_TYPE value, uint8_t mode)
{
    
	uint8_t i = 0;
	PARITY_CHECK_PACK_TYPE result = 0;
	uint8_t count = 0;
	for(i = 0; (value >> i) != 0; i++) {
    
		if((value >> i) & 0x01) {
    
			count++; // It is used for statistical integer conversion to binary 1 The number of  
		}
	}
	if(count % 2 == 0) {
     //1 The number of is even  
		switch(mode)
		{
    
			case 0:// Even check is adopted  
				// Last place to fill 0
				result = ((PARITY_CHECK_PACK_TYPE)value << 1);
				break;
			case 1:// Odd check  
				// Last place to fill 1
				result = ((PARITY_CHECK_PACK_TYPE)value << 1) | 0x01;
				break;
			default:
				return 0; 
		}
	} else {
    	//1 The number of is odd 
		switch(mode)
		{
    
			case 0:// Even check is adopted 
				// Last place to fill 1
				result = ((PARITY_CHECK_PACK_TYPE)value << 1) | 0x01;
				break;
			case 1:// Odd check 
				// Last place to fill 0
				result = ((PARITY_CHECK_PACK_TYPE)value << 1);
				break;
			default:
				return 0; 
		}
	}
	return result;
} 

/* * value:  Received data to be parsed  * mode : 1 Indicates odd parity ,0 Indicates even parity  *  Return value ： Data parsed with parity , Invalid data returned 0 */ 
PARITY_CHECK_DATA_TYPE ParityCheckRecieve(PARITY_CHECK_PACK_TYPE value, uint8_t mode)
{
    
	uint8_t i = 0;
	PARITY_CHECK_DATA_TYPE result = 0;
	uint8_t count = 0;
	for(i = 0; (value >> i) != 0; i++) {
    
		if((value >> i) & 0x01) {
    
			count++; // It is used for statistical integer conversion to binary 1 The number of  
		}
	}
	switch(mode)
	{
    
		case 0:// Even check  
			if(count % 2 == 0) {
    // If the data obtained 1 The bits of are even , Description is valid data  
				result = (PARITY_CHECK_DATA_TYPE)(value >> 1);
				return result;
			} else {
    
				return 0;
			}
		case 1:// Odd check  
			if(count % 2 == 1) {
    // If the data obtained 1 The number of bits of is odd , Description is valid data 
				result = (PARITY_CHECK_DATA_TYPE)(value >> 1);
				return result;
			} else {
    
				return 0;
			}
		default:
			return 0; 
	}
}

int main(void) 
{
    
	uint16_t input = 0;
	printf(" Please enter a number ：");
	scanf("%d", &input);
	printf(" The original value is ：");
	FuncOutputBin(input);
    printf(" The value after even check is ：");
    FuncOutputBin(ParityCheckSend(input, 0));
    printf(" The value after odd check is ：");
    FuncOutputBin(ParityCheckSend(input, 1));
    printf(" The value after parsing odd check is ：");
    FuncOutputBin(ParityCheckRecieve(ParityCheckSend(input, 1), 1));
    printf(" The value after parsing even check is ：");
    FuncOutputBin(ParityCheckRecieve(ParityCheckSend(input, 0), 0));
    return 0;
}

4. Operation result display

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