Re: [CAD_CAM_EDM_DRO] black box specs

Jeff, you can isolate the computers on your network in at least five
(simple) ways that I can think of:
1. Using subnets masks
2. Protocol bindings
3. Workgroup names
4. Use different network protcols
5. Direct (separate) cabling

Smoke

-----Original Message-----
From: GW <gggwood@...>
To: CAD_CAM_EDM_DRO@egroups.com <CAD_CAM_EDM_DRO@egroups.com>
Date: Thursday, December 07, 2000 7:43 PM
Subject: Re: [CAD_CAM_EDM_DRO] black box specs

><unlurk>
>
>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).
>
><lurk>
>
>> Jon,
>>
>> Congratulations on being the first flaming arrow archer.
>>
>> I've been designing PC interfaces for years and I'm not convinced any of
>> them are all that deterministic.
>>
>> I am thinking in terms of only the control PC and the motion box on the
>> "network". Also there would be no real reason to run a full TCP/IP stack
>> on this so a lot of the other noise could go away.
>>
>> Yes, this is a very half baked idea.
>>
>> Jeff
>>
>> >
>> >Ugh! Ethernet is specifically designed to almost NEVER be

deterministic.

>> >For the most part, it is fast enough that if you coordinated the message
>flow,
>> >and only had the control PC and the motion box there, it probably would
>> >work. Even still, there would be network management software that
>> >would be sending out multicasts saying "I'm so-and-so, and I'm here!"
>> >every second or so, and that would cause an occasional collision.
>> >
>> >Jon
>> >
>
>
>
>
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