Hi Anthony,

Sorry I've been so quiet (about a five hundred pages to proof-read and a
broken tester will do that to you).

Actually, that's exactly the method I use in "Programming and Customizing
the PIC Microcontroller".  The only difference is, instead of setting up a
delay of 1 msec before varying the output pulse period, I put in a delay
loop for the 1 and then It does work well and is easily expandable.

When I did it, I had four Servo outputs and got a step granularity of 20
usecs (which gives 47 different steps).  The longer delay (you could bring
it down to a 7 usec step granularity for 143 different steps) for a single
channel.  For each servo, I do a compare on the count to the loop count and
when they match, I make the pulse low.

How are you planning on doing this for greater than one servo?

Thanx for sharing this with us - I'm interested in seeing what you come up
with.

myke
    -----Original Message-----
    From: Anthony Clay <adctemp@HOTMAIL.COM>
    To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
    Date: Tuesday, July 20, 1999 3:47 PM
    Subject: Hey Myke! Web page update


    No real new documentation on the Pic-Flyer,  but my PIC projects section
has a new "advanced servo control techniques and algorithms" page.

    While brainstorming I came up with a way to control more servos with
less processor time (processor time being measured in percentages of one
full second.  I may have found a way to control lots of servos, more than
12, and only use 24% of the processor!  I did this by coming up with this
great idea:

    Instead of "looping" to generate timed delays, why not just use some
advanced interrupt handler to make better use of that wonderful tmr0.  The
interrupt would work like this:

    Begin interrupt (triggered by timer0 every 18mS)

        reload timer0 to overflow in 1mS
        Set the pulse output pin high and an interrupt_flag high
        Return from interrupt

        Main-line code

        Begin interrupt again (1mS later)
        Check to see if flag is high
            If so, generate the rest of the delay "manually" (If you are
using a *really* fast processor, 20MHz, try         generating the entire
pulse with an interrupt.
        Once the delay is over, set the output pulse low.
        Set up timer0 to return control in another 18mS
    Return from interrupt

    In a nutshell, the entire idea is to provide more execution time to the
main-line code, in the PICFlyer, my servo controller must also handle 2-wire
serial communications, ( a later project. )

    I posted the document to illustrate a technique I though would be a good
contribution to the list.  Speaking of the list, could someone please append
my name and site to David Tait's, now defunct, list of hobbyists?

    Login: at www.intcon.net/~jrclay
    Goto: PIC Projects
    Goto: Servo Controllers and algorithms

    I have not yet posted the code for the Serial-Parallel controller, just
a single servo controller,  I am still working the the method described
above

    Myke P. : Your comments please.