Conflict between 18B20 and interrupt display.

电子_畿

Conflict between 18B20 and interrupt display. [Copy link]

I wrote a program to measure the temperature of 18B20 using 51, and used a digital tube to display it. The display was scanned by a timer interrupt. The display program was good, and the temperature driver was perfect. But it didn't display properly when I put a 1.9 yuan. I searched on Baidu and found that there was a conflict between the interrupt and the 18B20 driver. But how to solve it? Has anyone done this before? Please give me some advice...

maychang

18B20 has strict requirements on operation timing, and usually, interruption is not allowed when operating 18B20. However, the reading and writing operation time of 18B20 is not very long (tens of microseconds), and the conversion time is long (about 1 second). Therefore, when reading and writing 18B20, interruption needs to be turned off, and interruption is turned on after reading and writing (conversion command), so that 18B20 can convert by itself. After the conversion is completed, the interruption is turned off and the temperature data is read, and the interruption is turned on immediately after reading. In this way, the interruption time is relatively short, and the display is slightly delayed, which is usually not noticeable.

胡火龙

The above is very accurate. It should be a problem of timing and interruption.

电子_畿

//Write a byte of data to DS18B20 void writeByte(unsigned char dat) { unsigned int i; unsigned char j; bit b; TR0=0; for(j = 0; j < 8; j++) { b = dat & 0x01; dat >>= 1; //Write "1", pull DQ down for 15us, then pull DQ high within 15us~60us to complete writing 1 if(b) { ds = 0; i++; i++; //Pull down for about 16us, the sign requires 15~60us ds = 1; i = 8; while(i>0) i--; //Delay about 64us, in line with the write time slot requirement of not less than 60us } else //Write "0", pull DQ down for 60us~120us ds = 0; i = 8; while(i>0) i--; //Pull down for about 64us, Sign requirement ds = 1; i++; i++; //The whole write 0 time slot process has exceeded 60us, so there is no need to delay 64us like writing 1} TR0=1; } //Read one byte of data, implemented by calling readBit() unsigned char readByte() { unsigned int i; unsigned char j, dat; dat = 0; TR0=0; for(i=0; i<8; i++) { j = readBit(); //The first to read is the lowest bit dat = (j << 7) | (dat >> 1); } TR0=1; return dat; } Is this right? Do you disable interrupts in the read and write functions in the driver? It seems not possible.

电子_畿

I set the temperature module to execute in the interrupt, and then put the display in the main function, and it works. Although it can achieve the purpose, it is not easy to use if other work needs to be done. So,,, I still don't know how to use it.

maychang

Why not disable interrupts before calling the write function and enable interrupts immediately after executing the write function? The same is true for calling the read function.

电子_畿

But, I tried it. It's really no different from the original. It's really annoying. Does anyone know the specific timing of 18B20? For example, how long does it take to reset, convert temperature, read temperature, etc.? It seems that it takes less than 1s. Newbie help!!!

maychang

DS18B20.pdf (276 KB, downloads: 15)

2013-10-13 12:44 上传

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maychang

For example, how long does it take to reset, convert the temperature, read the temperature, etc.? It seems that it will take less than 1 second.

电子_畿

What about the rest of the time? Are they all converting temperatures? Can we do other things during the rest of the time?

maychang

The 750ms is for temperature conversion, and there is no read or write operation, so the interrupt can be turned on to execute the operation in the interrupt routine, such as display. The interrupt cannot be turned on during the read or write operation. If an interrupt occurs during the read or write process and the interrupt operation is executed, the 18B20 operation timing will definitely be destroyed. There are nine operations behind, all of which are in the microsecond level. Turning off the interrupt in less than 1ms will affect the display, but the human eye usually cannot feel it because the time is very short.

电子_畿

while(1) { if(time_1ms>2) //digital tube display, { time_1ms=0; dis_one(); } TR0=0; temper=getTmpValue(); //read temperature command sendChangeCmd(); //temperature conversion command TR0=1; Is this right? It seems to have no effect.