I2C - Chip not responding

Jun 13, 2005 4 Replies
G

I have an I2C bus with a PIC6621 master and a 24LC512 EEPROM slave. It is working. I am trying to add a DS1307 and a DS2482 to the I2C bus, but I can't get any response from either of the latter. I can see the SCL and SDA lines on my Optascope (and admittedly, the Optascope just barely has the power to see a



100 kHz signal). When I send the I2C address, I can verify the 8 bit pattern of SDA, but when the slave is supposed to send an ACK by holding SDA low, all I see is a high NACK pulse instead. It appears that the slave is not responding, or choosing to send a NACK. I have verified the addressing of the DS1307 (0xD0) and the DS2482 (0x30), so I'm stuck. Any suggestions are welcome.

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P

What clock speed as this device can go up to 400KHz?

So I wonder what clock speed you are trying to run at as DS1307 at least is 100KHz MAX I2C clock rate (SCL).

Paul Carpenter | paul@pcserviceselectronics.co.uk PC Services GNU H8 & mailing list info For those web sites you hate
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J

It was initially set at 400 kHz, but now it is running at 100kHz; which I did manage to verify on the Optascope.

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G

see

and

I now have it working. I had two problems:

1) The DS1307 absolutely MUST have a battery connected 2) The very last read of the device must be NACKed by the Master
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S

Darn. I almost suggested this [1], but it didn't seem to fit the symptoms you described. Sorry.

[1] I also wasted a day or so staring at 'scope traces due to having missed this point in the specs...

Steve

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