Limit number of DIO devices under a DIO Main Ring

[keithkcchan]

What is the limit on number of DIO devices by utilize HSBY M580 on board DIO ports?

What about the limit if using BMENOC0321 on the HSBY M580 Racks? 

[Michael_Chan]

A HSBY system with a DIO ring can be constructed using

• BME NOS 0300 module. The CPU alone scans up to 64 DIO devices.
• One or more BME NOC 0301/11 modules to scan up to 128 devices.

DIO devices cannot be connected to the Remote I/O network. Connection to RIO main ring is possible through the service port of a CPU or a CRA adapter module, eNOC, eNOS Ethernet network option switch or a Modicon Switch (DRS).

[Michael_Chan]

The BME NOC 0321 control network module provides support for I/O scanning using EtherNet/IP and Modbus TCP.

NOTE: The maximum I/O scanning capability for a BME NOC 0321 module is 5,500 packets per second.

[Michael_Chan]

Combined EtherNet/IP Scanner/Adapter and Modbus Scanner:

[Richard]

The main limitation for a DIO ring using RSTP is going to be that for the protocol itself. The recommendation is for no more than 40 nodes, meaning that you can have 39 devices. This will be true for both the M580 and the BMENOC0321.

[RoozeeR · Accepted solution]

The previous answers are all correct. Knowing the maximum, you have to consider multiple items:

1: Maximum supported DIO devices:

HSBY CPU: 61 (max = 64, 3 are reserved for Ethernet/IP local slaves)

BMENOC0321: 112 (max = 124, 12 are reserved for Ethernet/IP local slaves)

Be aware that connecting DIO devices direct to the device ports of a HSBY CPU might not work as the CPU device ports have a VLAN active, which might not be supported by the device. To overcome this issue, use external switches or use BMENOS0200 switch in the CPU racks.

2: Maximum supported input/output size

HSBY CPU: 4Kbyte IN + 4Kbyte out (see previous answers)

BMENOC0321: 4Kbyte IN + 4Kbyte out (see previous answers)

Basically this means that the amount of data communicated is DIO device type dependent. You have to calculate the amount of data each device is communicating + take the overhead into consideration. I use to create some configuration and see what the data is used for each specific device type.

3: Maximum communication bandwith of an interface

HSBY CPU: 15000 packets

BMENOC0321: 5500 packets

The amount of packets is depending on the configured RPI (Repeat Packet Interval / Repeat Rate / update rate). For example when you define 100 devices with an RPI of 10 mS, will result in minimal 2(Read+write) * (1000/10) * 100(devices) = 20.000 packets. Solution will be to decrease the RPI for some/all devices, to keep the amount of packets between the limits.

4: Physical network limitation

When using a RSTP ring functionality, the limitation is to have max. 40 device within a ring. As  both CPU's count as a RSTP device, this limits the amount of DIO devices in a ring to 38. This imitation comes from fixed RSTP parameter settings in Schneider Electric DIO devices with RSTP functionality enabled (ie Modicon STB, Altivar Process). To overcome this limitation you can create a network star (using switches) or create multiple network rings (also by using switches) 

[keithkcchan]

Thank you all for the details explanations.

[keithkcchan]

Thank you all for the details explanations.

[keithkcchan]

Thank you

[keithkcchan]

Thank you for the information.

[HiDwivedi]

BMENOC0321: 112 (max = 124, 12 are reserved for Ethernet/IP local slaves) 

Can we assume this Limitation is for one port? In this case, BMENOC0321 will be supporting 2 port X112=224 Devices leaving service port spare.

Please confirm.

[Richard]

A couple of things:

The thread is for "Limit number of DIO devices under a DIO Main Ring". Obviously, to implement a ring you would need to use both ports.

If you were to implement two DIO clouds using the two ports, the total number of devices is dependent on the scanner not the port (see Michael's second post). This is for all ports and would still limit the total number of devices to 112.

If you want to connect more than 112 devices, don't forget that you can add multiple NOC modules to the configuration, each with its own scanner.

[HiDwivedi]

Thanks for the Information Richard,

I got a pretty much idea about the limitation, however here is something more I need your help to clarify, Can I use 1- Port of NOC0321 for acquiring the data from 112 Modbus TCP devices and 2nd port for connecting SCADA sending the data?

In this way, I want to collect data through one port and use the second port for SCADA Interface. Is it possible?

[Eric_Coudurier]

In a normal way the BMENOC0321 uses the 2 Control Network ports ETH2 ETH3 to communicate with the SCADA. The IO scanner is only performed on these ports(ETH2, ETH3), when the Service and the Backplane ports are configured to support IP forwarding (they are on different subnets).

In any case, it is possible to use the Control ports (ETH2 ETH3) to connect devices and SCADA but all the traffic will be on the same subnet.  Scada and devices will see all the traffic. Control Network port (ETH2 ETH3) is a dual port acting like as a switch.