Re: [CAD_CAM_EDM_DRO] Problem with Lindsay/Duncan DRO 5.1 program and IRQ interface

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, August 26, 2003 12:49 PM
Subject: Re: [CAD_CAM_EDM_DRO] Problem with Lindsay/Duncan DRO 5.1 program
and IRQ interface


> >When two encoders transition simultaneously (for example, moving both X
and
> >Y at the same time at a rapid pace), eventually the two axis will have a
> >transition extremely close together and the IRQ does not have time to
reset
> >after the transition from one axis before the transition from the other
axis
> >occurs. Thus, the IRQ 'misses' a transition, while the raw data catches
it
> >and the program counts this as an error (as it saw a data transition, but
no
> >IRQ transition) and loses the 'missed' movement.
> >
> >
> Well, this is obviously a total design flaw of the software!

That's my dad's opinion, I'm not sure that my setup is running the right way
(due to the different chips).

> What is the purpose of the IRQ mode? it seems like it reduces the
> reliability of
> the program. Still, I prefer to use dedicated hardware for this. My
> hardware
> can count up to 300,000 encoder counts per second on each axis,
> simultaneously.
> If that isn't fast enough, the digital filtering can be set for a
> shorter interval,
> and easily go to 1 million counts/second. With dedicated hardware, you
> don't
> have to worry about a CPU having to service a memory refresh or timer
> interrupt, it is always doing the exact task it is designed for, and
> never being
> 'borrowed' for any other task.
>
> The US Digital LS7166 chip is pretty similar to what I designed in my
> projects,
> and they are only about $11, I think. The interface to read them out is
> very
> simple, and 3 of them could be connected to a parallel port with minimal
> interfacing circuits. All you'd need are one decoder to select each chip
> separately.

From what I understand, the IRQ mode is so that the computer can just watch
the IRQ channel and when a transition is noticed, it will check to see what
transition occured and register that as movement. This lets the program
track movement while the program is on the menu screens and the like (the
IRQ mode also has the option of using a very nice looking 7-segment numeric
font, rather than just a large DOS font, but that requires lots of
processing power, so without the IRQ, a transition might be missed when
doing the display computations for the nice font), as it requires less
processing power to watch the IRQ than to watch all eight income bit streams
(two per axis, four axis possible).

John