Re: [CAD_CAM_EDM_DRO] black box specs

Point to point with a cross over cable.
Ethernet can't be beat. You can always just jam frames
out through the card sans-protocol. At 100Mb it will
be (in what Microsoft used to described CE/NT)
'real-time enough'. After all, the determinism is
coming from the stunt box not the PC. 'Where'
the determinism starts is not important as long as
it ends up where it 'needs' to be.

-G

----- Original Message -----
From: Jeff Barlow <jeff@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Thursday, December 07, 2000 10:32 PM
Subject: Re: [CAD_CAM_EDM_DRO] black box specs


> Hi "GW",
>
> I didn't say it was bad, just very half baked.
>
> Yes, CAN would be my first choice if we were talking about networking a
> bunch of boxes to do factory automation or some such. We're just talking
> about a way to connect a PC to one external box, no hub or switch, just
> one crossover cable.
>
> I'm not aware of any truly inexpensive CAN interfaces that plug into a
> PC. Ethernet NICs are hard to beat for price.
>
> BTW, I've heard the Microchip CAN chip is still pretty buggy. Also, in
> addition to Infineon (Siemens), you might have a look at the similar
> CAN/micros from ST and Fujitsu. They're all sort of overkill for this,
> though.
>
> Jeff
>
> On Thu, 7 Dec 2000 21:43:28 -0500, GW wrote:
>
> >
> >Jeff, it's not as bad as you think.
> >
> >Jon, with the exception of ATM (and Allen-Bradley's ControlNet), few
> >networks are deterministic. All are described in probabilistic.
> >I've worked with _many_ fieldbus type I/O system. Ethernet is
> >becoming very popular because of it price, ease of use, distances,
> >reliability, etc.. Probability is based on loading, network speed,
etc..
> >Do a quick lookup of industrial Ethernet, you may be surprised at what
> >is being done with it in real-time control environments.
> >
> >Jeff, you are correct that you would not have to attach a 'name brand'
> >protocol stack of any type. Likewise, most management traffic comes
> >from 'higher' layers such as Netware & Microsoft network clients which
> >you would not bind to those cards. Even if you did use a full blown
TCP/IP
> >stack, you'll see ARP traffic but if it is an isolated subnet that's all.
> >
> >Multiple devices are attached to a single subnet via a switch. With
100Mb
> >PCI Ethernet cards costing $20 and 10/100Mb 5 port Ethernet switches
> >costing $80, this is very economical.
> >
> >The only real problem is the complexity of creating you own protocol
> >stack so that you can use the NIC manufacturers low-level drivers.
> >Still eminently doable.
> >
> >Perhaps a better suggestion is CAN. Inexpensive CAN interfaces are
> >available. While not deterministic, collisions do not result in a loss
of
> >data.
> >CAN is the basis for DeviceNET which is a _widely_ used standard for
> >real-time I/O. No real need for the DeviceNET overhead (it's not that
much
> >tho)
> >and it is _very_ reliable and has a top speed of 1Mb. Microchip now
sells
> >CAN interfaces standalone (for a few bucks) and finally integrated with a
> >PIC.
> >Making a serial to CAN bridge would be walk in the park. They are
available
> >commercially for a couple hundred bucks from people like AB. There are
also
> >developer kits even cheaper. The CAN spec is free from BOSCH. As far
> >as the 'black box' side, more powerful processors with CAN integrated are
> >available (Siemens C167, C505).
> >>
>
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