Sensirion SHT71 with PIC18F2550

Marius H. Guest 2010-12-27 12:09 #1991049

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Hi,

I'm having problems interfacing a Sensirion SHT71 with a PIC18F2550. I 
want to measure the humidity and send it via EUSART to the PC, but I get 
nothing on the PC side. I've used the EUSART several times so that is 
not the problem. I've attached my assemblerlisting and I hope someone 
can help me.

Thanks in advance,
Marius

Attached files:

sht11.asm (7.6 KB) | highlighted code

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oli Guest 2010-12-28 15:53 #1992598

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You should use a scope an check out the communication step by step.
Get some Debug-Informations too. I guess you are using MPLAB. So check 
out the Debug-mode (View->Watch) It's very helpfull.

Btw: The error is hard to tell, if you dont name the problem more 
precisely.

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Marius H. Guest 2010-12-28 21:49 #1993048

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Unfortunately I don't have a scope. It seems like there's a problem with 
sending a command. On the ACK impulse I can see that the sensor pulls 
the DATA line low (line 144), but it doesn't pull it high afterwards 
like it's shown in the datasheet.

Attached files:

sht11.asm (6.47 KB) | highlighted code

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oli Guest 2010-12-29 09:24 #1993343

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my assembler isn't that good.
maybe it's a timing problem. try to slow the clock down. but it could be 
one of many things. you should really use that debugger and check all 
signals step by step.