On Fri, 26 Mar 2010 12:28:03 -0800, Robert Baer
wrote:

Spehro Pefhany wrote:
On Tue, 23 Mar 2010 21:15:02 -0400, the renowned "Oppie"
wrote:

I believe that you will find that the difference is in the different types
of digital inputs used on pins 7 and 8 of the MCU.
Look at pages 10-11 of the data sheet. Pin 7 (RA5) is 'ttl' input. Pin 8
(RE0) is a Schmitt Trigger TTL input. On pin 8, the Schmitt hysteresis is
giving the difference you observe.

Also look at the datasheet page 31 for details of the port structures and
how this might impact your design.

it is sometimes acceptable to use a digital input with an analog input. In
this case though, you should consider either using the analog input mode or
using an external comparator with well defined trip levels.
That's the 10 minute review, hope it helps - Oppie

Or switch to the PIC16F887 or other micro with two comparators
on-board. As typical with Microchip, the newer parts are also
considerably cheaper than the long-in-the-tooth PIC16F877 (way less
than half the price in 100's).



Best regards,
Spehro Pefhany
Then suggest a PIC that is supported by LDmicro and hasat least as
many usable pins.

Unless you're contracting me to do the work, that's your job, not
mine, but the one I did suggest should be a pretty good choice. In DIP
package, it has 40 pins, all of them start out as being usable.