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measuring temparature using ds1821[please helppp]

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umutguncan

umutguncan

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ds1821 asm

ı am using 8051 and assembly...
I want to measure temp and get it to R0....


I have a problem with signals..
İn datasheet there is a reset pulse and presence pulse.. Ok I give the reset signal to the bus but presence pulse????

please help me
 

Hi,

The presence pulse comes from DS1821. It is about 0.5msec Active Low pulse and indicating to the master (here your 8051) that it is ready to operate given an appropriate function command. So, after pushing low DQ line to Low (about 0.5msec-This is your reset pulse) you have to set your R0 to HiZ (High Impedance) and have to wait Presence Pulse will come from DS1821.. That's all..

Regards.
 

why ı have to set my r0 to hiz?
ı did not understand.. Can you help me more please??
 

Hi,

Here, HiZ means set the R0 as an input pin. In other words, set the output driver of R0 to HiZ mode.. Why you should do it? Because, in next step you need the read the level of DQ line.. If it is continuously High, it indicates that something is wrong.. But, If you can read DQ as Low about during 500msec(or maybe shorter), it is Presence Pulse that coming from DS1821. It indicates that DS1821 is alive and waits your function commands...

Regards.
 

u can use LM35 ,which is more easy to use
 

thanks dds
you say ?
if I want to set the bus LOW ı have to set the outpin of the microproccer HIGH???????
isnt it???
 

Hi,

Unfortunately NO...


Regards...
 

how can ı set the bus 0....
there is a pull up with vdd
 

in datasheet
write this
hold the bus 60ms low or hig etc..
how can ı hold the bus inlow please helppp

with 8051
 

make the coresponding pin output and put it in low state for 60us. then make it input again.
just read very careful the timing diagrams in the ds1821 datasheet. you will get the answers. remenber that in 1Wire bus is a bidirectional line and the timing is critical.
 

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