Best practice: IO in local 1756 chassis?

[thingstodo]

A ControlLogix backplane is a communications network, its proper name is ControlBus, although universally accepted as "backplane"... Modules connected to the backplane "communicate" on that network, using CIP, at a mere 5 MB/s.

Adding a 100 MB/s Ethernet module to the chassis, and using it for remote I/O will not give you a faster data-rate than 5 MB/s, since the data ultimately has to travel across the 5 MB/s backplane.

And don't forget that any remote chassis backplane also runs at 5 MB/s.

Are you sure about those numbers?

Adding a 100 MB/s Ethernet module (or several) to the chassis still requires the information to flow from the L73 to the EN2T over the backplane.

I had 5 L73's in one 17 slot chassis producing/consuming 4 arrays of 100 32-bit dints each, every 20 ms, alongside 3 controlnets that scheduled to >80% bandwidth. The enbts were used for a programming interface. Plus a couple of Prosoft cards that transfer blocks of ... 400 registers? .. every 40 ms. I dropped the RPI for the produced/consumed to 5 ms for testing ... and I never ran out of bandwidth on the backplane. I would have guessed the backplane to be >50 MB/s. To service even a couple of EN2Ts plus a couple of controlnet ... maybe 200 MB/s?

If RA limited the bandwidth on the backplane to 5 MB/s. That would only service one Controlnet?

 

[ASF]

Well, use 1 of those fingers for me. 5 CN2's, 5 L73's, 2 Prosoft serial cards, 5 ENBT/EN2Ts.

I knew someone would pop up. Which finger would you like?

 

[thingstodo]

I knew someone would pop up. Which finger would you like?

I am partial to the index finger

 

[daba]

Are you sure about those numbers?

Adding a 100 MB/s Ethernet module (or several) to the chassis still requires the information to flow from the L73 to the EN2T over the backplane.

I had 5 L73's in one 17 slot chassis producing/consuming 4 arrays of 100 32-bit dints each, every 20 ms, alongside 3 controlnets that scheduled to >80% bandwidth. The enbts were used for a programming interface. Plus a couple of Prosoft cards that transfer blocks of ... 400 registers? .. every 40 ms. I dropped the RPI for the produced/consumed to 5 ms for testing ... and I never ran out of bandwidth on the backplane. I would have guessed the backplane to be >50 MB/s. To service even a couple of EN2Ts plus a couple of controlnet ... maybe 200 MB/s?

If RA limited the bandwidth on the backplane to 5 MB/s. That would only service one Controlnet?

Bandwidth calculations on the backplane are difficult because it, and the rest of any I/O system, use the CIP EtherNet/IP protocol of produced/consumed data. I may be wrong, but always believed the maximum data-rate on the backplane "ControlBus" to be 5MB/sec, but haven't found any supporting documentary evidence.

5 or perhaps 50, but definitely no-where near your 200 MB/s suggestion.