I2C - Chip not responding

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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.



Re: I2C - Chip not responding
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What clock speed as this device can go up to 400KHz?

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

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--
Paul Carpenter          | snipped-for-privacy@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/ PC Services
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Re: I2C - Chip not responding
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It was initially set at 400 kHz, but now it is running at 100kHz; which I did
manage to verify on the Optascope.




Re: I2C - Chip not responding
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see
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and
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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





Re: I2C - Chip not responding
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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
http://www.fivetrees.com



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