> -----Original Message-----
> From: Kevin Blain [SMTP:kevinb@WOODANDDOUGLAS.CO.UK]
> Sent: Monday, March 19, 2001 9:24 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: [PIC]: I2C pullups
>
> When you TRIS a pin as input, then read it, does that not put a logic 1 in
> the PORT register if the pin is pulled up? If so, when the pin is TRIS'd
> to
> output again, it will be outputting logic 1.??
>
The port latch is only changed if a Write or Read Modify Write instruction
is executed on the port.  So if a pin is set as an input, and then a BSF/BCF
etc is performed on the port, the port latch for that pin will be set to
whatever state the pin is at.  This won't happen by simply reading the state
of the port however.

Regards

Mike


> Therefore, care should be taken when doing I2C in this method to make sure
> that the pin is set to output 0 whenever you tris back to an output.
>
> Regards, Kevin.
>
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