Howard....

I don't think the docs mean not to read. You couldn't do anything then. See
page 31 of the current f873 data sheet. Each time you test a bit it must
read the D flip-flop to know what the state of the INPUT is. A change flag
is set if and only if the change DFF is EXOR with the previous value at
that pin....I think. Agree the data sheet is somewhat confusing.

To make sure, I'd simply try each case, writing a simple program, and
changing the various inputs. The convoluted docs will then become
clear...i.e. writer's intent.

Phil.


On Wednesday, May 10, 2000 9:50 AM, Howard McGinnis
[SMTP:hmcginni@DIGITAL.NET] wrote:
> Hello,
>
> I'm using a 16F873 in an application and plan to use PORTB as 5 inputs, 3
> outputs with the inputs being bits 3-7 to take advantage of the interrupt
> on change feature. The docs caution against reading the port which is
> understandable.
>
> Does the PIC do a read-alter-write when executing a BSF or BCF
instruction
> or does it have the ability to set or reset a bit directly? Does using
> PORTB in this mixed mode screw up the interrupt on change?
>
> Thanks,
> howard
> Howard McGinnis
> hmcginni@digital.net
> Electronic Visions, Inc.
> 1650 Barrett Drive
> Rockledge FL 32955
> (321) 632-7530
> http://ddi.digital.net/~hmcginni
> mcginnis@e-visions.com