>I am curious about your statement, Andrew. Can you please tell me more
>about the problems involved in PORTB interrupt on change?
>I was just reading a manual page about "interrupt on change" when your msg
>was delivered to my box..!

In brief, the PORTB interrupt on change feature is not intended for use as a
general purpose multiple interrupt source.  This is because you can affect
the PORTB status with ANY operation that accesses ANY bit on the port
(though I'm not sure about "movf", but I would assume so because the port is
read).

From the 16C71 datasheet:

"This interrupt on mismatch feature, together with soft-
ware configurable pull-ups on these four pins allow
easy interface to a keypad and make it possible for
wake-up on key-depression. Refer to the Embedded
Control Handbook, "Implementing Wake-Up on Key
Stroke" (AN552).
The interrupt on change feature is recommended for
wake-up on key depression operation and operations
where PORTB is only used for the interrupt on change
feature. Polling of PORTB is not recommended while
using the interrupt on change feature.
Note: For the PIC16C71
if a change on the I/O pin should occur
when the read operation is being executed
(start of the Q2 cycle), then interrupt flag bit
RBIF may not get set."

I feel that Microchip doesn't make as big a deal out of this as they should.
  They simply say "polling of PORTB is not recommended."  If you use this
feature as they suggest, for wake up on keypad input, then you can use the
interrupt feature during sleep and disable the interrupts during polling,
which would work great.  If you don't use it for this purpose, but instead
try to use it for multiple general purpose interrupts while using the
remaining PORTB pins for other purposes, you will invariably run into a heap
of trouble trying to track down why your interrupts are working "more often
than not, but not always."

--Andrew
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