Raspberry pie 4B learning notes - IO communication (1-wire)

Introduction to single bus protocol

1-wire Single bus is Maxim Wholly owned subsidiary Dallas A proprietary technology of . With most current standard serial data communication methods , Such as SPI/I2C/MICROWIRE Different , It uses a single signal line , Transmission clock , It also transmits data, and the data transmission is bidirectional . It has the advantage of saving I/O Port line resources 、 Simple structure 、 The cost is low 、 It is convenient for bus expansion and maintenance .¹
The data transmission rate of single bus is generally 16．3Kbit/s, Up to 142 Kbit/s, Usually, we use 100Kbit/s Transmit data at the following rate
1-Wire The line port is the port of open drain structure or three state gate , Therefore, it is generally necessary to add a pull resistance Rp, Generally selected 5K~10KΩ.
For the detailed introduction of single bus, please refer to This article .
Participate in the blue bridge cup or use it through MCU DS18B20 My classmates must be familiar with this agreement , The step used in the process of obtaining temperature is to initialize , Then write the order ; And then initialize , Read the command to get the temperature . Communication steps of the whole single bus ： initialization 1-wire device 、 distinguish 1-wire Devices and exchange data .
Because they are master-slave structures , Only when the master calls the slave , Only the slave can answer , So the host accesses 1-wire Devices must strictly follow the single bus command sequence , namely 1. initialization 、2.ROM、3. command Function command .

Used today DHT11 He just uses the single bus data format , Specific command sequence and DS18B20 These strictly follow initialization 、ROM、 The components of the command trilogy are different .DHT11 Only the communication steps of single bus ： initialization 1-wire device 、 distinguish 1-wire Devices and exchange data .

Raspberry pie 4B+DHT11（1-Wire agreement ）

DHT11 brief introduction

Interface definition

data format

DATA foot For microprocessors and DHT11 Communication and synchronization between , Use single bus data format , Primary communication time 4ms about , The data is divided into decimal part and integer part , The specific format is explained below ：
8bit Humidity integer data +8bit Humidity decimal data
+8bi Temperature integer data +8bit Temperature decimal data
+8bit The checksum

When the data transmission is correct, the check sum data is equal to “ 8bit Humidity integer data +8bit Humidity decimal data
+8bi Temperature integer data +8bit Temperature decimal data ” The end of the result 8 position .

Communication process

1. Bus initialization ;（ Pull down the bus for no less than 18ms, Then release , Bus returns to high level ）
2.DHT11 The reply ;（DHT11 The answer pulls the bus down ）
3. Output data frame （ A complete data transfer is 40bit, High first out .）
Data frame format :
Communication sequence diagram ：

Hardware connection

Raspberry pie	DHT11
5V	vcc
7 Pin No ( Onboard code )	DATA
GND	GND

Start raspberry pie 1-Wire Interface

This step is the same as before SPI、I2C Same operation , No more maps , For the sake of insurance , It is suggested to open the mouth and restart the raspberry pie sudo reboot.

Programming to realize

because DHT11 The reading of is relatively simple , Is to control according to the sequence IO Input and output of the port .
Code from This article .
The author simply added notes according to the sequence diagram
open Geany, Enter the following code ：

// An highlighted block
//
//mydht11.c
//
#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
 
typedef unsigned char uint8;
typedef unsigned int  uint16;
typedef unsigned long uint32;
 
#define HIGH_TIME 32
 
int pinNumber =7;  //use gpio1 to read data(wPi code )
uint32 databuf;
 
 
 // Read the value of the sensor 
uint8 readSensorData(void)
{
    
    uint8 crc; 
    uint8 i;

    pinMode(pinNumber,OUTPUT); //  Set the pin to output mode （ Used to control bus level ）
    digitalWrite(pinNumber, 0); //  Pull down the bus （ Start signal ） 
    delay(25);//（ The starting signal shall not be less than 18ms Low level of , Here the author uses 25ms）
    digitalWrite(pinNumber, 1); //  Host releases bus （ Bus returns to high level ）
    pinMode(pinNumber, INPUT); //  Set the pin to input mode , It is convenient to detect the response signal of the slave 
    pullUpDnControl(pinNumber,PUD_UP);// Set as pull-up input .
 
    delayMicroseconds(27);
    if(digitalRead(pinNumber)==0) // Check whether the bus is pulled down by the slave , If you pull it down, it means that the slave answers .
       {
    
         while(!digitalRead(pinNumber)); // Flag waiting for data transmission from the slave （ Pull high ）
 
	  for(i=0;i<32;i++)// Read 32 Is the temperature and humidity data 
	   {
    
	   while(digitalRead(pinNumber)); //data clock start
	   while(!digitalRead(pinNumber)); //data start
          delayMicroseconds(HIGH_TIME);
          databuf*=2;// Carry is equivalent to a left shift in a bit operation .
           if(digitalRead(pinNumber)==1) //1
 	       {
    
                databuf++;
 	       }
	    }
 
	  for(i=0;i<8;i++)// Collect 8-bit parity data 
	   {
    
	   while(digitalRead(pinNumber)); //data clock start
	   while(!digitalRead(pinNumber)); //data start
          delayMicroseconds(HIGH_TIME);
          crc*=2;  
          if(digitalRead(pinNumber)==1) //1
	       {
    
                crc++;
	       }
	    }
	return 1;
       }
   else
        {
    
        return 0;
         }
}
 
int main (void)
{
    
 
  printf("Use GPIO1 to read data!\n");
 
  if (-1 == wiringPiSetup()) {
    
    printf("Setup wiringPi failed!");
    return 1;
  }
 
  pinMode(pinNumber, OUTPUT); // set mode to output
  digitalWrite(pinNumber, 1); // output a high level 
 
  printf("Enter OS-------\n");
  while(1) {
    
    pinMode(pinNumber,OUTPUT); // set mode to output
    digitalWrite(pinNumber, 1); // output a high level 
    delay(3000);
    if(readSensorData())
    {
    
       printf("Congratulations ! Sensor data read ok!\n");
       printf("RH:%d.%d\n",(databuf>>24)&0xff,(databuf>>16)&0xff); 
       printf("TMP:%d.%d\n",(databuf>>8)&0xff,databuf&0xff);
       databuf=0;
     }
    else
     {
    
        printf("Sorry! Sensor dosent ans!\n");
       databuf=0;
      }
  }
  return 0;
}

The effect is as follows ：

Using single bus and DS18B20 Communication obtains temperature

Because the big guys have already made DS18B20 Read file , So I'm using DS18B20 When obtaining temperature , Just call the file interface to get the temperature information , There is no need to think STM32 Like other monolithic devices, it initializes the sequence diagram bit by bit , Writing data / Instructions , Read the data .c Language implementation detailed steps reference This article ;Python Reference resources This article .

summary

The use of single bus is recorded here , If there is something wrong, you are welcome to criticize and correct .

Wire Basic principle of single bus

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