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tmp102

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Linuxbuilders

Joined: 20 Mar 2010
Posts: 193
Location: Auckland NZ

tmp102

Posted: Sat May 16, 2015 3:23 am

Just in case if anybody is having problems with a code for tmp102 and negative values here I put mine:

Code:

long tmptt;
float tmptf;
int tmp01;
int tmp02;
short neg;

//read temperature 12 bit value

i2c_start();
i2c_write(0x90);
i2c_write(0x00);
i2c_start();
i2c_write(0x91);
tmp01 = i2c_read();
tmp02 = i2c_read();
i2c_Stop();

tmptt = make16(tmp01,tmp02);
tmptt = tmptt >> 4;
if (tmptt > 0x7FF)
{
tmptt = ~tmptt+1;
neg = 0; //negative value
}
else
{
neg = 1; //positive value
}
tmptt = tmptt * 0.0625;
tmptf = tmptt;

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PCM programmer

Joined: 06 Sep 2003
Posts: 21708

Posted: Sat May 16, 2015 11:05 am

Quote:

i2c_start();
i2c_write(0x90);
i2c_write(0x00);
i2c_start();
i2c_write(0x91);
tmp01 = i2c_read();
tmp02 = i2c_read();
i2c_Stop();

You are missing the NACK on the last read, and that is part of the TMP102
specification. See page 12 in the TMP102 data sheet, and look at this
diagram: Figure 9. Two-Wire Timing Diagram for Read Word Format
http://www.ti.com/lit/ds/symlink/tmp102.pdf
The data sheet is poorly written in this area. It shows an ACK by the
master (the PIC) on the last read. But then down in notes 2 and 3,
it says the master (the PIC) should leave SDA high to terminate a one
or two-byte read operation. This is a NACK !

The Philips i2c specification says on page 10, in section 3.16:

Quote:

When SDA remains HIGH during this ninth clock pulse, this is defined as
the Not Acknowledge signal.

http://www.nxp.com/documents/user_manual/UM10204.pdf

So you should do a NACK on the last i2c_read(). This is done by giving
the function a parameter of 0.

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