A-B DeviceNet Communication

It's it better to locate a 1771-SDN DeviceNet card in the main chassis vs. in a remote rack (RIO)? Or, does it make any difference?

I have a PLC5/40 with a remote I/O rack that contains the 1771-SDN but I was expecting the communications to be of a higher speed. I realize DeviceNet is a non determistic network. I was wondering since I am using a remote I/O network to talk to the rack, if I eliminate the jump could it increase the update rate. The network is 500k baud, polled 1ms and currently only communicating to two non A-B motion controllers.

Thanks.

Yes, you will get a lot faster throughput if you put the devicenet scanner in the CPU chassis.

Block transfer to a module over RIO is limited to the speed of the RIO bus. So it will be a major bottleneck on the Devicenet speed.

Block transfer to a module in the CPU chassis goes over the chassis backplane, and as such is much faster.

Experiment with the two solutions, and see how different the block transfer "done" bits updates. You dont have to have any IO connected.
Remember to post your findings.

Yes, definitely put the SDN in the chassis with the processor for a major speed increase.

Also, make sure you only program the block transfers you need to get the data to/from the SDN. If you put in the 62, 61, 60, 59, etc. transfers but are only really using less than 62 words then you are wasting time transferring empty blocks of data.

WARNING!!

Also, note that if you use the additional block transfers that steve708 mentions (which you will want to if you want the node status information from the scanner) DO NOT configure the DeviceNet scanner through the IO Configuration utility from inside RSLogix 5!!! skuller

Your additional block transfers from the 1771-SDN will not work properly and the data will not be correct.

Darren

Good input

Thanks all for your input, it is appreciated. I will see if I can move some I/O around and put the SDN in the main chassis. I was suspecting that it would be better.

Now let's just hope I shuffle around enough to free up a slot!

If there is a power supply that resides in one of the chassis slots, then you can free that slot by exchanging the power supply for an external one.