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'[PIC]: I2C - 16F877 Some chips not responding.'
2000\08\20@060837 by Chamberlain

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Help please. I seem to have a problem with 2 of my I2C chips. After receiving help from Andy Stubbins I now have the 877 talking to my 24LC65 Eeprom via the  I2C MSSP. The clock and thermometer chips do not respond. The I2C pcb was moved from a 16F84 test pcb to the 877 test pcb so I know it works. I wondered if the other chips do not support 400Khz mode so I changed to 100Khz. I started the '877 at 20Mhz but changed to 4Mhz adjusting the setup as I went. I now have 2 pluggable xtals. They both work OK, 877 starts, LCD displays a message from eeprom . I am using 22k pull-ups and have added 2 more in parallel to reduce the resistance and test the signal rise time. I used converted code, pin bashing the I2C pins to test the electronics which worked. Any ideas why these other two chips do not respond??

Thanks in advance. Chris Chamberlain.

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2000\08\22@024329 by Chamberlain

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Apologies to all. It seems that I got a brace in my tag instead of a bracket, damn painful.
Any way I still need help. Any clues will do.

I seem to have a problem with 2 of my I2C chips. After receiving help from Andy Stubbins I now have the 877 talking to my 24LC65 Eeprom via the  I2C MSSP.  The clock and thermometer chips do not respond. The I2C pcb was moved from a 16F84 test pcb to the 877 test pcb so I know it works. I wondered if the other chips do not support 400Khz mode so I changed to 100Khz. I started the '877 at 20Mhz but changed to 4Mhz adjusting the setup as I went. I now have 2 pluggable xtals. They both work OK, 877 starts, LCD displays a message from eeprom .  I am using 22k pull-ups and have added 2 more in parallel to reduce the resistance and test the signal rise time. I used converted code, pin bashing the I2C pins to test the electronics, which worked.
I have re-tested the circuit back on the '84 pcb and it still works. Any ideas why these other two chips do not respond??
Is it possible that the pull-ups are too high? Phillips' spec says 1.7k.

Thanks in advance. Chris.
Beam me up .I am sick of this I2C stuff. It worked OK on the 16f84.

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2000\08\22@080346 by Olin Lathrop

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>>
I am using 22k pull-ups and have added 2 more in parallel to reduce the
resistance and test the signal rise time. I used converted code, pin bashing
the I2C pins to test the electronics, which worked.
<<

That sounds very high for the speeds you are trying to attain.

> Phillips' spec says 1.7k.

So what are you doing using 22K?!

Try running the IIC VERY slowly to see if it is a basic functional problem
or a speed problem.  Of course when you are violating the spec by more than
an order of magnitude, all bets are off.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, spam_OUTolinTakeThisOuTspamcognivis.com, http://www.cognivis.com

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