Re: Jog wheel

["marc" <dfs-at-xmission.com>]

----- Original Message -----
From: "j riach" <jamie-at-riach.com>
To: "Multiple recipients of list" <emc-at-nist.gov>
Sent: Tuesday, June 04, 2002 7:42 AM
Subject: Re: Jog wheel


>
> On Tuesday 04 June 2002 12:24 am, you wrote:
> > ----- Original Message -----
> > From: "William Scalione" <scalion-at-dellepro.com>
> > To: "Multiple recipients of list" <emc-at-nist.gov>
> > Sent: Monday, June 03, 2002 3:49 PM
> > Subject: Re: Jog wheel
> >
> > It does not have to be that big of deal.
> > Less than 5 bucks will get you a "PIC" or Atmel uController that would
> > easily
> > do this. All you'd need to do is add a MAX232 TTL<->RS-232 Level
converter
> > for $1.50 and you'd be set add all the switches indicators and
handwheels
> > you
> > want quite cheaply.
> >
>
> > Marc Christensen
> the rs-232 interface is even more at risk than the parports we use?
> in this case one of the fddi usb to parallel adapter chips (looks to a
> peripheral like a fifo buffer ) and some logic would be good. But how
> would servicing the usb stack affect performance ? on a windows system
there
> is a noticeable drop in response even if my scanner and camera are only
> connected and sitting idle.
>

I think there are 2 approaches to that problem.
First, define a standard communication record format and protocol API
and stick to it. By doing that the physical hardware in the Pendant and
the driver program for the PC can be modified to run over whatever
physical means necessary to talk without messing up the rest of the system.
This is good practice anyway.

Then look at all the specialty hardware that uses uses RS-232 and will
continue
to do so for many years and the fact you will probably be able to buy CHEAP
serial adapters for the next 10 years. I would really prefer to toast a
multi IO
card than the USB/Firewire driver chips on the motherboard.

My approach would be to use one uController to manage the communication and
connect it right AT the PC and run RS-485 line xcvrs to the pendant which
has its
own uController or go straight to fiber optics running at the same RS-232
type speeds.
Lots of controllers will run sync serial protocols I'd either do that or set
up a constant
handshaking protocol between them and do an immediate ESTOP if the
connection
is ever lost.


Marc