Most flexible field bus communication for hot swap

[Chris Elston 79]

I am looking for a property in some field communications that I have not seen yet. For example, which field communications (device net, profibus, control net, or other) can be unplugged from the network and the master scanner will ignore the slave device that has just been unplugged? I'd like to make a modular cell that can be plugged into a main PLC system, auto detect that the module was plugged into the PLC system. If the module was plugged in, then start executing the PLC code for that module. The field communication needs to be flexible enough to do this "hot" with no power down from the master, and the master needs to auto detect the slave has entered the network so it can start polling it with information and executing PLC code for that module. I've done device net before, but it didn't seem that flexible to do what I asked above. Can profibus do this? I have not done a profibus system yet to know if profibus supports this. I am almost thinking about just slapping a micro controller on the “modular” cell and just handshake go/busy signals with it…..but it would be neat to do this will a field bus communications if any of them support this.

[panic mode 246]

CC Link (open) and AB Remote I/O (propriatery) come to mind.

[Jay Anthony 118]

Omron masters for both Devicenet and Profibus do exactly what you want to do - that is, hot patch new nodes into the system at will and withdraw them at will. This is because they have the ability to build a scan list or device list on the fly. Must be 2 bytes in and 2 bytes out or less. Omron also has a small mivro which has a built in DeviceNet slave interface (CPM2C) with built in I/O. Makes a nice intelligent slave, if you need an extral serial port or two.

[Chris Elston 79]

Seems to me Remote I/O faulted when the communcation was unplugged from the scanner card or a PLC5. Are you sure about this PanicMode? Maybe I didn't have some setting turned on or something. Care to expand?

[Chris Elston 79]

Ooo....that sounds neat and exactly what I asked for. What did you mean by the two bytes? Just status bits that need to be polled by the master to check and see if the slave is out their on the network?

[panic mode 246]

I am not sure about PLC5 but on SLC system I used ca year ago I had no problem. Actually I did have a problem - I couldn't tell that one of the field nodes was down.

[Jay Anthony 118]

Actually in this automatic scan list mode, each node number gets allocated two bytes of input and two bytes of output as real world I/O. If your device has more than this configuration, then it will be allocated multiple node numbers until its requirements are satisfied. If you have to have all 63 nodes, then you must use configuration software. Those who use the Omron Devicenet and Profibus masters love this feature. Micron Semiconductor uses these Devicenet masters inside their fabs and technicians don't have to get suited up for inside fab work because the operators just unplug the machines and roll them around the fab. They have as many as five masters on a single PLC for about a total of 5000 I/O points per PLC.

[Sleepy Wombat 27]

I hav'nt used 5000 I/O on Devicenet but the configuration of plug and play with the Omron Devivenet I have used in a similar way to Jays example and it worked well. The Omron Devicenet Master is the easiest to set up that i have used. (I auto config, no setup required).

[KinK 0]

Ya I agree Omron Device net is awsume you can plug and play or buy the configerator and use it that way really smooth operation. ps They have just come out with a new modual DRT2 apparently you can pull even more info Like bus voltages and other neat stuff right from the slave..... Edited 4 May 2004 by KinK