Hello Everyone,

I thank everyone for taking time out to guide me in my problem.

My apologies to you all for troubling you.

I used a different oscilloscope probe and found out that the signals are 
going towards 0V (less than 0.8V) with sharper edges.

All these days the other probe was performing well. Now I have thrown it 
into the dustbin.

At low frequencies, the probe was performing well. At higher frequencies 
the probe was misbehaving.

Happy PICking.

Ravi

On 09/07/2010 7:05 PM, Michael Rigby-Jones wrote:
>
>
>> -----Original Message-----
>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
> Behalf
>> Of Ravi
>> Sent: 09 July 2010 13:46
>> To: Microcontroller discussion list - Public.
>> Subject: Re: [PIC] Strange behavior of PICmicro I/O pin
>>
>> Spehro,
>>
>>> You have set the relevant SCL/SDA port bits to 0 and are writing to
> the
>>> TRIS registers, not the port registers, to control SCL/SDA, right?
>>
>> Below is my initialisation code.
>>
>> initialise	clrf porta
>> 		clrf portc
>
> Spehro is not referring to your initialisation code, but the way in
> which you are manipulating the port pins when sending data/clock
> signals.  I2C is an open collector bus system; when "bit bashing" an I2C
> master interface you set the output data latches low and leave them.
> You then set the TRIS bit to 0 to output a low state, and the TRIS bit
> to 1 to output a high state (the resistor pulls the pin up to Vdd).
>
> However, the fact that you see this issue with no EEPROM connected makes
> me think this is not the problem.  What it does sound suspiciously like
> is your PIC does not have its Vss pin(s) grounded properly, and is
> instead grounding through one or more of the ESD protection diodes.
> This could certainly explain the voltage offset when the pin is low.
>
> Regards
>
> Mike
>
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