TRISA on 16F819

[Dennis Owen]

When I write 255 to TRISA on the 16F819 I get the following on
a read operation. 11011111. I know that RA5 is multiplexed for
other functions but no matter what I do I still get the same thing.

[PCM programmer]

In the 16F819 data sheet, look in the section on I/O ports.
In that section, there is a block diagram for each pin.
For RA5, it shows the "RD TRIS" signal is connected to a
buffer, whose input is tied to Vss (ie., Ground).
Furthermore, it doesn't even show a TRIS flip-flop.
You can't set TRIS on that pin. It's always an input.

However, based on what you've said about always reading
a zero for TRIS on that pin, I would say that the block
diagram has an error. It shows Vss feeding into an
inverting buffer. This would make it always read a "1".
Since you're reading a zero, it's likely that it's really
a non-inverting buffer, or it could be that the buffer's
input is tied to Vdd instead.