DS18B20 single bus data transmission

　　A pure single-chip microcomputer cannot do much, and must be equipped with various peripherals. Therefore, it is essential to understand the data communication between the single-chip microcomputer and the sensor. Common single-chip microcomputer data communication methods include SPI, IIC, RS232, single bus, etc. Each communication method has a corresponding timing diagram. Analyzing the timing diagram and completing the code writing is a compulsory course for single-chip microcomputer learners. This article takes DS18B20 as an example to analyze single bus data transmission.

　　DS18B20 uses a single bus for data transmission, so the timing requirements are very high. It is very necessary to learn how to analyze its timing diagram.

　　1. Initialization timing diagram analysis:

　　First, the bus controller pulls the bus down for 480us. After 480us, the bus is released and the pull-up resistor pulls the bus up. After waiting for 5-60us, the DS18B20 starts to respond and pulls the data bus down for 60-240us. After that, the bus is released and the pull-up resistor pulls the bus up. The converted code is as follows:

　　u8dsbInit() // Initialization, return 0 means DS18B20 has no response, otherwise it has a response

　　{

　　dsbDQStat(0); //Controller pulls down the bus

　　delay500us(); //Pull the bus down for a while

　　dsbDQStat(1); //Release the bus

　　delay60us(); //wait for DS18B20 response

　　if(dsb_DQ) // if there is no response, return 0 directly

　　{

　　return0;

　　}

　　delay240us(); //If there is a response, wait for the response to end

　　return1; //Return to initialization state

　　}

　　2. Read the timing diagram analysis:

　　First, the controller pulls the bus down for >1us, then the controller releases the bus. If the controller samples a low level at this time, the read value is 0, if it is a high level, the read value is 1. Note that there is a 15us marked in the figure, which means that the controller sampling is completed within 15us. After 15us, the bus is pulled up by the pull-up resistor and maintained for 45us. The entire read cycle is 15+45=60us. The time of this cycle must also be controlled. The conversion code is as follows:

　　u8dsbReadByte() //Read a byte of data, starting from the low bit

　　{

　　u8i,tmp=0;

　　for(i=0;i<8;i++)

　　{

　　dsbDQStat(0); //Controller pulls down the bus

　　tmp>>=1; //Start reading from low bit

　　dsbDQStat(1); //Release the bus

　　if(dsb_DQ)tmp|=0x80;

　　delay15us();

　　delay45us(); //control cycle time

　　}

　　returntmp;

　　}

　　3. Write timing diagram analysis:

　　First, the controller pulls the bus down for 15us. After that, if you want to write 0, the bus will continue to be pulled down for 45us. If you want to write 1, the bus will be released and the pull-up resistor will pull the bus up for 45us. The write sequence is relatively simple and can be converted into code as follows:

　　void dsbWriteByte(u8dat) //Write a byte of data, starting from the low bit

　　{

　　u8i;

　　for(i=0;i<8;i++)

　　{

　　dsbDQStat(0); //Controller pulls down the bus

　　delay15us(); //maintain 15us

　　if(dat&0x01)dsbDQStat(1);

　　elsedsbDQStat(0);

　　dat>>=1;

　　delay45us();

　　dsbDQStat(1); //Release the bus after 45us

　　}

　　}

　　The three timing diagrams of DS18B20 have been analyzed. DS18B20 is just an example of single-bus data communication. Now that you have learned the analysis of the DS18B20 timing diagram, you can try to analyze the DHT11 timing diagram to complete its initialization function and data reading function.