I2C - Chip not responding

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.

On Monday, in article <GXkre.47768$wr.42953@clgrps12>
     nochancey@mrwhalen.com "Gavin Jacobs" wrote:
>I have an I2C bus with a PIC6621 master and a 24LC512 EEPROM slave. It is

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

>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

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

>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.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
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Paul Carpenter wrote:
> On Monday, in article <GXkre.47768$wr.42953@clgrps12>
>      nochancey@mrwhalen.com "Gavin Jacobs" wrote:
>> I have an I2C bus with a PIC6621 master and a 24LC512 EEPROM slave. It is
>
> What clock speed as this device can go up to 400KHz?

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

"Gavin Jacobs" <nochancey@mrwhalen.com> wrote in message news:GXkre.47768$wr.42953@clgrps12...
>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.
>

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

"Gavin Jacobs" <notasnoball@inhell.com> wrote in message 
news:WCrre.49352$on1.21736@clgrps13...
>
> 2) The very last read of the device must be NACKed by the Master

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