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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