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SDA left low after i2c_stop()

 
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e_vandyke
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SDA left low after i2c_stop()
PostPosted: Fri Dec 14, 2007 11:15 am     Reply with quote

I'm currently trying to read some I2C devices using an 18F8722 PIC, using the current version of the CCS compiler.

I am able to perform a standard combo write/read cycle once, but after completing the cycle, the I2C hangs at the i2c_write() call in the next combo write/read cycle (executing the exact same code).

My i2c configuration spec is:
#use i2c(MASTER,SLOW,SCL=SCL1,SDA=SDA1,FORCE_HW,RESTART_WDT) // MSSP #1

and my write/read cycle is coded as:
printf("i2c_start...");
i2c_start();
printf("write addr...");
i2c_write(addrH); // Select sensor
i2c_write(addrL); // Select sensor
printf("write reg...");
i2c_write(regSel); // Select read register
i2c_write(dataAddr); // Select data address
i2c_start(); // Restart
i2c_write(addrH|1); // Select sensor [1st byte only, RD]
z = i2c_read(); // Read msB
z = (z << 8) | i2c_read(); // Read lsB
y = i2c_read(); // Read msB
y = (y << 8) | i2c_read(); // Read lsB
x = i2c_read(); // Read msB
x = (x << 8) | i2c_read(); // Read lsB
i2c_stop();

Any ideas?
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri Dec 14, 2007 11:25 am     Reply with quote

You need to do a "NAK" on the last i2c read. This is done by using 0x00
as the parameter for i2c_read(). Example:
Quote:

x = (x << 8) | i2c_read(0); // Read lsB
i2c_stop();


If that doesn't fix the problem, then post the manufacturer and part
number of the Sensor device.
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