I2C blues

[mackrackit]

I am sure you have checked, but are the connections to A0-A1-A2 solid?
That output makes me wonder.

[circuitpro]

You have the address configured as device 5. PortD.6 is SDA, PortD.5 is SCL. Is that correct? I always use 4.7K pullups on the I2C lines too. You might try making them a little less stiff.

[Bill Legge]

Suggest you check:

1. 4.7k pull-ups not 2.2k - may not make any difference but will elliminate a possibility. I know 10k pull-ups work at low speed but not 40MHz.

2. Address you are using is: 101, are the chip pins set accordingly?

3. A 512k EEPROM must have a word size address, is XX definately a word size variable?

4. Is the write-protect pin grounded to enable writing?

Regards Bill Legge

[Charles Linquis]

I tried 10K pull-ups (no joy) and my program scanned all the addresses.

For X = 0 to 7
Address = $A0 + (X<<1)
...

The internal device address ("command") was definitely a WORD variable.

But I *DID* find something very interesting: Whenever the MSb (A2) of the EEPROM was brought high, the device stopped responding. Addresses $A0,$A2,$A4,$A6 all worked. $A8,$AA,$AC and $AE didn't. This happened on two separate devices (both were Microchip 24FC512's from the same lot).

Tomorrow AM, I'll find out more.

And for those playing with I2C, I found out the hard way that if you invoke DEFINE I2C_HOLD 1 and something holds SCL low (like a remote device with a diode clamp to ITS Vcc and it loses power), there is no timeout. Your program hangs forever. An email to MELABS support got me a quick answer (from a familiar person). Solution: if you are using the HOLD option, test for SCL HIGH before you invoke any I2CWRITE command.

[Bill Legge]

CL,

What is a 'MCC I2C analyzer?'

Regards Bill Legge

[Charles Linquis]

http://www.mcc-us.com/MIIC-101-DS.htm

[Bill Legge]

CL,

Thanks - I've had a look at the site/product - a bit pricey for me as only an occasional/hobby I2C user. The Australian magazine 'Silicon Chip' had an I2C analysis board as a do-it-yourself project about a year ago. It used pretty mendane chips and some free Phillips software; I must give it a go.

Can you run your system at 10MHz and see if that does the trick?

Please let us know when/if you get it going. I spent ages getting familiar with EEPROM I2C and would like to learn what the problem was.

Regards Bill legge