Learning notes of raspberry pie 4B - IO communication (I2C)

GPIO signal communication

That was mentioned before GPIO Input detection and output control , Now record about raspberry pie GPIO Communication function , In embedded I2C、SPI、UART Is the most commonly used communication protocol , Through these protocols, we can communicate with many master-slave devices , Use today I2C Of 0.96 " OLED Screen as an example , Use the raspberry pie that comes with it I2C Interface to drive OLED The screen shows what we want to show .
Here is a little knowledge about the agreement ：
full duplex ： You can receive data or send data You can do it at the same time ----------- Two data lines
Half duplex ： You can receive data or send data It cannot be done at the same time ------- A data cable
Simplex ： You can only receive data or send data ---------------------------- A data cable

Serial ： Data bit by bit transmission --------- One line transmits data

For example, we will mention I2C、UART.
parallel ： Data is transmitted all at once --------- Multiple lines transmit data

For example, the camera in smart car competition adopts parallel communication .（ The above pictures are from This article ）
field bus ： It can be transmitted over a long distance can （10km） 485（1km） // Differential mode signal
Commonly used in industrial control .
Board level bus ： Communication between chips ---- A little distance IIC SPI // Common mode signal
General communication mode between components .
Synchronous communication ： Both communication parties use the same clock source （ clock frequency ）
asynchronous communication ： Both communication parties use their own clock source
The specific classification of communication is shown here post .

I2C brief introduction

I2C It is a two-way two-wire bus launched by Lipper ,SCL Clock line and SDA cable , For data transmission , According to the knowledge points mentioned above I2C yes Serial half duplex board level synchronous wired Transmission bus .
One bus mounts multiple IIC Interface devices ----- Parallel connection at IIC On the bus .
About a group I2C How many buses can be connected at most I2C Devices and I2C For your reference This blog post

of I2C The transmission flow of , I've seen it before and thought that bloggers made an analogy between the whole process and playing football , I think it's very image , here link Share with you

of I2C Please refer to the above blog for detailed knowledge of , The author will not make an analysis here , Let's go to the topic ： Using raspberry pie I2C.

Raspberry pie 4B+0.96OLED(I2C agreement )

Query interface

Open terminal command , Input gpio readall, enter , In the returned IO You can see in the table SDA1、SCL1;SDA0,SCL0 Two groups I2C Interface , We use SCL1 And SDA1 This group carries out .

Hardware connection

The wiring is as follows ：

Raspberry pie	OLED
5V	VCC
GND	GND
3 foot （SDA1）	SDA
5 foot （SCL1）	SCL

With raspberry pie I2C Interface

For those who have an interface or are not used to the command line, it is recommended to skip the following section , Refer to the interface .

There is no interface or you want to use the command line

Use putty perhaps Xshell Log in to raspberry pie , At the terminal command input sudo raspi-config, enter
Enter the following interface .

Use the keyboard to select up and down 3.Interface Option, enter , Use the keyboard to select up and down I5 I2C enter ;

Keep going back ;

Continue to enter ;

Use the right mouse button to select finish, enter , Return to the command window ;

Input sudo reboot, Restart raspberry pie .

There is an interface

open Raspberry Pi Configuration

Open it as shown below I2C.

Then select logout ;Reboot Wait for restart .

wiringPiI2c library

Library profile

Same as before IO The input and output are the same , You also need to install the corresponding library to realize the function . of wiringPiI2c Library functions and STM32 I2C The common functions of are compared as follows ：

wiringPiI2c	STM32
wiringPiI2CSetup (const int devId) ;	peripherals nit(void); Initialize peripherals
wiringPiI2CReadReg8 (int fd, int reg)	iic_read_byte(void); Read one byte of data
wiringPiI2CWriteReg8 (int fd, int reg, int data)	iic_send_byte(u8 data)// Send a byte of data

For a detailed description of this library, refer to this link .
You can find wiringPiI2CSetup (const int devId) There's a parameter in , Combine the above kicking analogy and I2C Theoretical knowledge of , We know that this parameter is the address of the slave , In raspberry pie, you can pass i2detect Command to query the address of the peripheral , To use this command, you need to install i2c-tool.

install i2c-tool

Open the terminal command input ：sudo apt-get install i2c-tools enter , Wait to return to the command line again .（ You need to make sure your raspberry pie has a net ）

Inquire about I2C The address of the peripheral

Enter at the command line ： sudo i2cdetect -l enter , The following display appears , The description uses I2C1 Interface .

Then input ： sudo i2cdetect -y 1, enter , The following display will appear , there 3C Namely OLED The address of （ Now raspberry pie I2C Do not connect other devices ）, General 0.96 " OLED The address of the screen is 0x30.

Programming effect

Through the above comparison , We know the whole I2C The function of is just replaced by the function interface of raspberry pie , We will usually use I2C The effect can be achieved by replacing the corresponding function in the screen driver , The specific replacement process can be referred to This article .
open Geany, Enter the following code （ Because the mold is too long, you need to go to this link to download the link ：https://pan.baidu.com/s/13SFd-MNfgJ1wD3R3np0T4w
Extraction code ：yjyx
Yes C standing VIP You can also download it directly , I set it up. 0 Download points , The name of the resource is raspberry pie 4BIICOLED The screen ）：

// An highlighted block
#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<unistd.h>
#include<assert.h>
#include<termios.h>
#include<string.h>
#include<sys/time.h>
#include<time.h>
#include<sys/types.h>
#include<errno.h>
#include <wiringPi.h>
#include <wiringSerial.h>
#include <wiringPiI2C.h>
#include <unistd.h>
typedef unsigned          char uint8_t;
typedef uint8_t  u8;
#define OLED_CMD   0x00
#define OLED_DAT   0x01
int fd;                                 
unsigned char  yi[16]={
    "Angle of beam:"};
unsigned char  er[16]={
    "ming"};
unsigned char san[16]={
    "Distance:"};
unsigned char  si[16]={
    "okok"};
const unsigned char zi[];
const unsigned char picture1[];
const unsigned char picture2[];
const unsigned char picture3[];
const unsigned char picture4[];
const unsigned char picture5[];
const unsigned char picture6[];
const unsigned char picture7[];

void WriteCmd(unsigned char I2C_Command)
{
    
   wiringPiI2CWriteReg8(fd,0x00, I2C_Command);
}
// Drawing point function 
void OLED_SetPos(unsigned char x, unsigned char y) 
{
     
   WriteCmd(0xb0+y);
   WriteCmd(((x&0xf0)>>4)|0x10);
   WriteCmd((x&0x0f)|0x01);
}
//BMP Bitmap display 
void OLED_DrawBMP(unsigned char x0,unsigned char y0,unsigned char x1,unsigned char y1,unsigned char BMP[])
{
    
   unsigned int j=0;
   unsigned char x,y;

 if(y%8==0)
   	y = 0;
 else
   	y += 1;
   for(y=y0;y<y1;y++)
   {
    
   	OLED_SetPos(x0,y);
   	for(x=x0;x<x1;x++)
   	{
    
   		 wiringPiI2CWriteReg8(fd,0x40,BMP[j++]);
   	}
   }
}


void init(void)//OLED initialization 
{
    
   wiringPiSetup();
       fd=wiringPiI2CSetup(0x3c);//i2c?
       wiringPiI2CWriteReg8(fd,0x00,0xa1);//t?í??90xa0
       wiringPiI2CWriteReg8(fd,0x00,0xc8);//L?úí??90xc0
       wiringPiI2CWriteReg8(fd,0x00,0x8d);//A?5w?
       wiringPiI2CWriteReg8(fd,0x00,0x14);
       wiringPiI2CWriteReg8(fd,0x00,0xa6);//óí?>:90xa7
       wiringPiI2CWriteReg8(fd,0x00,0xaf);// >:
}

void qingping(void)// Clear the screen 
{
    
   char zt1,zt2;
   for(zt1=0;zt1<8;zt1++)
   {
    
   	wiringPiI2CWriteReg8(fd,0x00,0xb0+zt1);
           for(zt2=0;zt2<128;zt2++) wiringPiI2CWriteReg8(fd,0x40,0x00);
   }
}


void ascii(float Angle,float distance)// Character display function 
{
    
   sprintf(er,"%f",Angle);  // float 0 char
   sprintf(si,"%f",distance); // double 0 char 
   int zt;
       char zt3,zt4;
   for(zt3=0;zt3<4;zt3++)
       {
    
   	wiringPiI2CWriteReg8(fd,0x00,0xb0+(zt3*2));
               for(zt4=0;zt4<16;zt4++)
               {
    
   		         for(zt=0;zt<8;zt++)
                       {
    
                       	if(zt3==0) wiringPiI2CWriteReg8(fd,0x40,zi[yi[zt4]*16+zt]);
                               else if(zt3==1)  wiringPiI2CWriteReg8(fd,0x40,zi[er[zt4]*16+zt]);
                               else if(zt3==2)  wiringPiI2CWriteReg8(fd,0x40,zi[san[zt4]*16+zt]);
                               else if(zt3==3)  wiringPiI2CWriteReg8(fd,0x40,zi[si[zt4]*16+zt]);
                       }
   	}
               wiringPiI2CWriteReg8(fd,0x00,0xb0+(zt3*2)+1);
               for(zt4=0;zt4<16;zt4++)
               {
    
               	for(zt=0;zt<8;zt++)
                       {
    
                       	if(zt3==0) wiringPiI2CWriteReg8(fd,0x40,zi[yi[zt4]*16+zt+8]);
                               else if(zt3==1)  wiringPiI2CWriteReg8(fd,0x40,zi[er[zt4]*16+zt+8]);
                               else if(zt3==2)  wiringPiI2CWriteReg8(fd,0x40,zi[san[zt4]*16+zt+8]);
                               else if(zt3==3)  wiringPiI2CWriteReg8(fd,0x40,zi[si[zt4]*16+zt+8]);
                       }
               }
   }
}


int main()
{
    
   float Angle = 2.98754546;
   float distance = 5.754644545;

   init();
   delay(10);
   qingping();// Clear the screen 
   delay(10);
   ascii(Angle,distance);// Character display 
   delay(10);
   	
   while(1)
   {
    
   	//qingping();
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture1);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture2);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture3);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture4);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture5);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture6);
   	delay(1);
   	OLED_DrawBMP(0,0,128,8,(unsigned char *)picture7);
   	delay(1);
   }
}

Then name and save , I think the previous code has been placed on the desktop too messy , So I created a new folder , Put the code in the folder , You can do it according to your own needs .

Because I changed the directory, the compilation time also changed
Input is ：cd Desktop/my_program/c（ Switch to the directory where I saved the files ） enter
Then input gcc -o display display.c -lwiringPi Compile and generate the execution file enter
Last sudo ./display enter After running, you can see the following effects .

It may be due to I2C Not fast enough , It makes you look uncomfortable , I'm going to change it later SPI Try your screen again , For the mold taking method, please refer to this article post Just go , You can also chat privately about the author's document tutorial .

summary

I want to put Bing Dwen Dwen , But the official doesn't allow it to be related to Bing Dwen Dwen , Those who want to see the effect can go B I'm looking at it from the website .