I've had some problems like this. Reading the I2C spec of the 24xxx
EEPROM, I noticed that you cannot read the recently stored value
immediately after a write cycle to the E2PROM, you have to keep sending
its address over the I2C buss until it signals an ACK, then it is ready
for another operation (it can accept a burst write, it has a buffer -
don't remember its size - so you may send several bytes at once, but
you'll have to wait much more time till it gets available again).

I have also noticed that the ACK is very important to get to know if the
EEPROM is really "understanding" what was sent to it, so if you get a
NOACK, send the data again.

Edward Cooper wrote:

> Hi
>
> If someone could help me here, I'm trying to get I2C up and running
> using a 24LC256 and a 16F877, I've put some code together mainly
> chopped bits of other peoples code!  However it doesn't work, when I
> read the data back from the EEPROM all I get is 1's, now in the data
> sheet when reading you are meant to issue a start command send the
> control byte address high and low byte and then issue another start.
> It won't let me do this (it gets stuck) so I issue a restart instead
> however this doesn't seem to work.
>
> Basically Im asking what is the difference between these two different
> commands!?
>
> Thanks for any help
>
> Ed Cooper
>
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