http://members.aol.com/JohnShaw/pid/index.html
has a good discussion of PID control including, one page down, a pseudo-code
implementation. I haven't personally tried it but the explanation is quite
clear and it might help.

-----Original Message-----
From: Koh Teik Siong <tsk196@soton.ac.uk>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Tuesday, December 16, 1997 12:38 AM
Subject: PID algorithm II


>HI
>        I am new to the PICLIST. I am now presently trying to implement a
PID
>controller and a trajectory motion control. I have look up the Embedded
>Control Book,AN532, and it has a very good reference. But the problem is
>that there are so many interrupts and function. Does anyone know of a
>simpler way of writing the PID algorithm?
>        Presently, I have a PIC which calculates the velocity and the
position
>of the motor. But how am I going to get the info from the PIC?
>Especially when it is has a 8-bit output for the velocity and position.
>        Another question is that can I use the same crystal for both my
PIC?
>        Thanks, with regards,