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Industrial Communication ProtocolsWhite Paper

Introduction to ModbusModbus communication protocol is a messaging structure developed by

Modicon in 1979. It is used to establish a master-slave or client-server

communication between intelligent devices. The intelligent devices

can be a PLC, HMI, PC, Distributed Control Systems (DCS), Supervisory

Control and Data Acquisition Systems (SCADA) etc. Modbus protocol is

not industry specific and can be used in a wide variety of industries such as

factory automation, building automation, process control, oil & gas, traffic

& parking, agriculture & irrigation, water & wastewater, pharmaceutical and

medical, material handling etc.

Modbus protocol can be operated via the

following communication methods:

• Modbus RTU or Modbus over serial – This

communication method or interface can

be RS-485, RS-232, RS-422 and RS-423.

Generally, in this interface, the Modbus

devices would require the receive wire (RX),

the transmit wire (TX) and the ground wire

(GND) to exchange data between the Modbus

devices. The interface can be either half

duplex or full duplex. Typically, all intelligent

devices can be configured for both half duplex

and full duplex.

• Modbus™ TCP/IP – In this communication

method, the Modbus data is wrapped around

TCP/IP internet protocols and then the data is

transmitted over standard internet. A standard

RJ45 Ethernet port can be used to connect

the various devices for data transfer. Modbus™

TCP/IP can be defined as an open standard

implementation of Modbus on internet

protocols.

• EtherNet/IP™ - EtherNet/IP™ is an

application layer/industrial protocol that is

built on the standard TCP/IP stack, where

TCP means transport control protocol and

IP means internet protocol (IP). EtherNet/

IP™ uses standard Ethernet hardware and

operates over Ethernet using the common

industrial protocols (CIP) – ControlNet &

DeviceNet and the TCP/IP protocol stack.

Although EtherNet/IP™ was developed by

Rockwell Automation for its Allen Bradley

line of controls, it is now considered an open

standard and is managed by Open DeviceNet

Vendors Association (ODVA).

FIGURE 1. ETHERNET/IP™ APPLICATION LAYERS

FTP HTTP OPC CIP Modbus SNMP

UDP

OSPF

ARP

IGMP

RARPIP

IEEE 802.3 Ethernet

IExplicitMessaging

ImplicitMessaging

EthernE 802 33

ExplicitMessaging

TCP

Application

Transport

Network

Data LinkPhysical

– PAGE 2 –

Industrial Communication Protocol White Paper

It is to be noted that the WMPR receiver only uses “Explicit Messaging” for

exchange of non-cyclic and non-time critical data between the devices

in the EtherNet/IP™ network. Explicit messaging uses the TCP/IP stack

and has a request/reply or client/server relationship. The client sends a

request to the server and the server responds to the request. This request

can be either read/write in nature. In our world, the client device can be

either a fieldbus coupler module or a host controller device and the server

device is the WMPR receiver module.

Note: For more information on Modbus™ RTU, Modbus™ TCP/IP and

EtherNet/IP™ please refer to www.modbus.org; www.rockwellautomation.

com & www.odva.org

Data Exchange between wireless receivers – WDRR/WMPR and Fieldbus Couplers WMPR Series: The WMPR Series is a reliable DIN rail or panel-mountable

wireless receiver that can accept 14 digital signals (PNP or NPN type) from

wireless Limitless™ switches or accept 14 analog signals from wireless

analog sensors. The WMPR receiver is menu driven through the use of

function buttons and an easy-to-read LCD display. The LCD menu allows

the user to see the nodes status, configure nodes and update receiver

functionality.

The WMPR receiver has EtherNet/IP™ as the

communication protocol. That means, it can

push all of the relevant information such as

nodes I/O Status (both digital and analog), unit

types of analog signals, battery level indication,

radio frequency signal strength, radio transmit

power type, field device type, radio transmitter

type, sensor update rate, IP address etc. through

the EtherNet/IP™ output. It has a standard RJ45

Ethernet port which needs to be connected to

the RJ45 port of the fieldbus coupler via a Cat5e

(twisted pair) or Cat 6 (standard) Ethernet cable

to establish data communication between the

two devices.

If the end user wants to display the data in a

host controller such as a PLC or HMI that has

Modbus™ TCP/IP protocol, then it is required

to connect the fieldbus coupler to the host

controller via a Cat5e or Cat 6 (standard)

Ethernet cable.

FIGURE 2: DATA EXCHANGE BETWEEN WMPR AND ETHERNET/IP™ OR

MODBUS™ TCP/IP NETWORK

Fieldbus CouplerEthernet IP or

Modbus TCP/IPNetwork

Honeywell WirelessSystem

PLC

– PAGE 3 –

Industrial Communication Protocol White Paper

To interface the WMPR with a host controller device, it is required that the

WMPR is connected to an EtherNet/IP™ compliant host controller and

upload the electronic data sheet (EDS) of the WMPR to the host controller

device. This step allows the object model of the WMPR to transition into

the electronic datasheet (EDS) which allows the unique MAC ID of the

WMPR to be associated with the various parameters of the object model.

The WMPR Object Model (Figure 3 - WMPR Object Model) describes the

different object models such as common objects, the application objects

and the assembly objects.

Common Objects include: Identity Object, Message Router Object,

Connection Manager Object, Parameter Object and Link Objects

FIGURE 3: WMPR OBJECT MODEL

Note: For more information on the WMPR Object

Model, please refer to the document “EtherNet/

IP™ Object Mode, P/N 32308916” on the

Honeywell website.

For the latest version of the EDS file, please refer

to the Honeywell website.

WDRR Series: The WDRR Series is a reliable DIN

rail or panel-mountable wireless receiver that

can accept 14 digital signals (PNP or NPN type)

from wireless limitless switches. The WDRR

receiver then communicates the digital signals

which is basically the wireless limitless switch’s

status i.e. whether the switch is open or closed to

a host controller device such as a PLC, DCS and

SCADA that has physical I/O modules. It also

has an output for lost RF communication and

another output for low battery voltage.

Once the WDRR receiver obtains the status

of the digital input of the Limitless™ switch,

the information is replicated in the WDRR’s

output terminals. Then it is required to hardwire

the output terminals of the WDRR receiver

to individual input terminals on the WAGO or

Beckhoff fieldbus coupler or any host controller

device with physical I/O modules.

Connection Manager Object(06)

IdentityObject

(01)

ParameterObject Instances

(0F)

MessageRouter Object

(02)

Link Object F6TCP/IP F5

AssemblyObject Instances

(04)

ApplicationObject Instances

(various)

ExplicitMsg I/O

– PAGE 4 –

Industrial Communication Protocol White Paper

FIGURE 4: DATA EXCHANGE BETWEEN WDRR AND MODBUS™ TCP/IP

NETWORK

Inpu

ts

Out

puts

WDRR Receiver Modbus TCP/IP

SS3(Sensing/Switching Device 3)

SS2(Sensing/Switching Device 2)

SS1(Sensing/Switching Device 1)

Modbus TCP/IP Network

PLC

Note: For more technical information on the WDRR and WMPR receiver

modules, please refer to the device’s datasheet on the Honeywell website

http://sensing.honeywell.com

When to use WMPR vs WDRRThe usage of WMPR vs WDRR is very application specific and may be

dependent on an existing control systems layout. To understand this

better, let’s take a look at the following real time application scenarios.

• If a customer already has a Fieldbus Coupler or some type of host

controller device such as a PLC or HMI, almost 90 percent of the time,

a Fieldbus Coupler/PLC/HMI will have some type of communication

protocol such as EtherNet/IP™, Modbus™ TCP/IP, Modbus™ RTU or

Profinet. In these types of system settings, the WMPR would be an ideal

candidate as it supports EtherNet/IP™ protocol.

However, there are many generic PLCs and Fieldbus Couplers out there

in the market that do not support any type of communication protocols.

These PLCs/Fieldbus Couplers can only support hardwire I/O signals

whether it is digital, analog, temperature, etc. In this type of scenario the

WDRR would be a good alternative.

• Generally, the cabinets which house control system hardware such as

Fieldbus Couplers, PLCs, I/O Modules, Power Supplies, Relay Module,

etc. are very heavily wired (Figure 5). In these types of settings, the

WMPR would be perfect as there is no wiring involved for Inputs and

Outputs. The status of all of the 14 digital/analog outputs from the

WMPR will be communicated to the host controller via a single standard

Ethernet cable. Less wiring will make the control system cabinet safer,

easy to identify parts and less time consuming for troubleshooting if

necessary.

However, if there is ample space available

for wiring in the control cabinet and if the

existing controllers do not support any type of

communication protocols, then WDRR would be

a very good alternative.

• Say a customer has a Fieldbus Coupler or

a PLC that is currently running on protocol

EtherNet/IP™, then another option might be

needed. Typically, these types of devices have

two to four RJ45 ports available per device.

If there are other Ethernet systems such as

a VLAN Networks, PC, DCS system, SCADA,

etc. already plugged in to the 4 available RJ45

ports of the Fieldbus Coupler/PLC, then there

is no RJ45 port available for the WMPR device.

In this scenario, the WDRR would come in

handy, as the Fieldbus Couplers/PLCs has

the ability to add I/O racks into an existing

controller.

• WMPR can support both analog and digital

signals. WDRR can only support digital

signals. So, for wireless applications involving

Honeywell’s wireless pressure sensors

(WPS Series), the WMPR would be the

recommended receiver module. Furthermore,

the WMPR would enable an operator to

change the update rate of the WPS series

analog sensors over wireless. This can be

a huge benefit especially if the sensors

are installed in places that are not easily

accessible.

– PAGE 5 –

Industrial Communication Protocol White Paper

• For autonomous time-critical applications, the WMPR would be a

perfect fit. The WMPR receiver module supports EtherNet/IP™ protocol

which is much faster than any existing serial communication protocols.

The WMPR can provide a wide variety of data points such as nodes

device status, I/O status, battery life indication, and network signal

strength which is typically required by a host controller to automate a

wireless network.

FIGURE 5: CONTROL SYSTEM HARDWARE

WAGO fieldbus coupler specifications: Fieldbus coupler part numbers (Factory recommended)

• Bus controller module: 750-352

• Power supply module: 750-602

• I/O module: 750-1405

• End module: 750-600

• Protocols: EtherNet/IP™, Modbus™ TCP/IP

• Baud rate: 10/100 Mbit/sec, full or half duplex

• Buscoupler connection: 2 x RJ45

• Number of I/O modules: 64

• Number of digital inputs per I/O module: 16

(PNP or NPN)

Note: For more technical information on the

WAGO fieldbus coupler, please refer to the

device’s datasheet at WAGO website http://www.

wago.us. There are many options available for the

bus controller module, power supply module, I/O

module and the end module.

FIGURE 6: WAGO FIELDBUS COUPLER WAGO Modbus™ TCP Coupler

Ethernet cable tomodbus network

Ethernet O/P fromHoneywell WMPRreceiver to WAGOcoupler RJ45

Digital input wired from HoneywellWDRR receiver

WAGO PN 750-352ETHERNET™ TCP/IP FIELDBUS

CONTROLLER WAGO PN 750-60224 VDC POWER SUPPLY MODULE WAGO PN 750-1405

16 CHANNEL DIGITAL INPUT MODULE(Can accept up to 64 I/O modules, thereby

supporting up to 1024 digital inputs)

WAGO PN 750-600END MODULE

For more informationsensing.honeywell.com

Honeywell Sensing and Productivity Solutions 1985 Douglas Drive North

Golden Valley, MN 55422

1-800-537-6945

www.honeywell.com

Beckhoff Fieldbus coupler specifications: Fieldbus coupler part numbers (Factory recommended)

• Bus controller module: BK9000/BK9050

• Power supply module: Built into the bus controller module

• I/O module: KL1154

• End module: KL9010

• Protocols: EtherNet/IP™, Modbus™ TCP/IP

• Baud rate: 10/100 Mbit/sec, full or half duplex

• Buscoupler connection: 1 x RJ45

• Number of I/O modules: 64

• Number of digital inputs per I/O module: 4 (PNP/NPN - configurable)

Note: For more technical information on the Beckhoff fieldbus coupler,

please refer to the device’s datasheet at the Beckhoff website https://www.

beckhoff.com . There are many options available for the bus controller

module, I/O module and the end module.

FIGURE 7: BECKHOFF FIELDBUS COUPLER

KL9010BECKHOFF

Ethernet O/P from Honeywell WMPRreceiver to Beckhoff coupler RJ45

Digital input wired from HoneywellWDRR receiver

Output to modbusnetwork

Beckhoff Modbus™ TCP Coupler

Ethernet TCP/IP BK9000,BK9050 Digital Input KL1154, KL1164

Configuration interface

Address selector

Ethernet RJ 45

BK9000, BK9050 I Ethernet TCP/IP Bus Couplers

Beckhoff PN BK9050(Can accept up to 64 I/O terminals and

one end terminal)

Beckhoff PN KL1154(4-channel digital input terminal)

Beckhoff PN KL9010(End terminal)

Top view Top view

Power-LEDs

K-bus

Power contacts

Input forpower contacts

Ethernet RJ 45

Signal LED1Signal LED3

Input 1

Power contact+24 V

Power contact DV

Input 3 Input 4

DV

+24V

Input 2

Signal LED4Signal LED2

KL9010System Terminals

BK9000 BK9050

+60° C

-25° C

Both of the fieldbus couplers namely – WAGO

and Beckhoff have the ability to accept digital

signals from the WDRR receiver. All of these

fieldbus couplers are designed for fieldbus

communication in both EtherNet/IP™ and

Modbus™ networks. The fieldbus couplers have

standard RJ45 Ethernet ports. So it is possible

to transfer the Limitless™ switches I/O status to

a host controller via protocols EtherNet/IP™ or

Modbus™ TCP/IP as long as the host controller

supports either of these two protocols. A Cat5e

(standard) or a Cat 6 (twisted pair) cable can be

used to connect the fieldbus couplers to a host

controller device.

Limitless™ is a registered trademark of Honeywell International Inc. EtherNet/IP™ is a registered trademark of ODVA, Inc.Modbus™ is a registered trademark of Schneider Automation Inc.

002415-1-EN | 1 | 02/2016© 2016 Honeywell International Inc.

Industrial Communication Protocol White Paper