>I was assuming that a read only operation would not affect the data in the
>port latch- although it doesnt say that specifically- but the last bit
>"care
>should be taken ... changing the direction from an input to an output" just
>confuses things further- or do they mean doing a RMW operation and then
>changing TRIS, in which case the caution doesnt really apply?

I guess I missed the original question.  But I can give an example of how
this can cause problems:

Pretend you're using passive I2C communication where the SCL and SDA lines
are being pulled up.  You load "0" into the latches for your SDA and SCL
pins.  Now you want to set the SCL line high, so you TRIS the pin to an
INPUT.  Now it's being pulled HIGH, even though your latch is still a "0".
Now you want to set the SCL line low, so you TRIS the pin back to an OUTPUT.
  Everything's fine.

Now, pretend you have an interrupt set and it goes off BETWEEN the two steps
described above (i.e., you're still in an INPUT mode).  Now somewhere in the
ISR, you happen to use a "BCF" on another pin of the same port.  This will
redefine your SCL latch to a "1" because of the RMW operation on the other
pin.  So, you have to "use caution when changing from an input to an output"
because of the possible unknown state of the port latches.  Note that it's
not a "READ" operation, per se, but a "BCF".  A pure READ operation will do
nothing to the port pin values itself, but it WILL redefine the port
latches.

Note that this is just one example of how things can go bad.  But I think
you can draw a parallel to your specific situation, assuming that your
application has any problems at all with these operations.

--Andrew

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