(12) United States Patent
`Dube' et al.
`
`USOO6434157B1
`(10) Patent No.:
`US 6,434,157 B1
`(45) Date of Patent:
`Aug. 13, 2002
`
`(54)
`(75)
`
`(73)
`
`(21)
`(22)
`(51)
`(52)
`(58)
`(56)
`
`MODBUS PLUS ETHERNET BRIDGE
`
`Inventors: Denis W. Dube, Pelham; Andrew G.
`Swales, Windham, both of NH (US);
`Cynthia Davies, Lowell, MA (US)
`Assignee: Schneider Automation, Inc., North
`Andover, MA (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Notice:
`
`Appl. No.: 09/167,251
`Filed:
`Oct. 6, 1998
`Int. Cl................................................. H04L 12/28
`U.S. Cl. ........................................ 370/401; 370/402
`Field of Search .................................. 370/401-405
`
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`Primary Examiner Melvin Marcelo
`ASSistant Examiner Ron Abelson
`(74) Attorney, Agent, or Firm Michael J. Femal; Larry I.
`Golden
`ABSTRACT
`(57)
`A bridge is disclosed for providing a connection between a
`MODBUS Plus network and an Ethernet network. The
`bridge includes a MODBUS circuit board, an Ethernet
`circuit board, and a CPU. The MODBUS circuit board is
`operably coupled to the local area network for receiving a
`message from an originating node having a five-byte routing
`path field. The CPU is operably connected to the circuit
`board for extracting a table location in response to a third
`byte within the routing path field. The Ethernet circuit board
`is operably connected to the CPU and the Ethernet network
`for forwarding the message to an IP destination in response
`to the table location.
`
`26 Claims, 12 Drawing Sheets
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`TCPip
`NTERFACE
`
`BRIDGE
`8 DATA PATHS
`8 PROGRAM PATHS
`
`MODBUS PUS
`NTERFACE
`
`18
`
`10
`
`16
`
`MODEUSPLUS
`
`
`
`
`
`MOBUS PUS
`BRIDGE
`
`ADDITIONAL
`MODBUS PLUS
`NETWORKS
`
`Page 1 of 21
`
`

`

`US 6,434,157 B1
`Page 2
`
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`ICS Instrumentation & Control Systems-Windows NT for
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`
`Page 2 of 21
`
`

`

`US 6,434,157 B1
`Page 3
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`
`Page 3 of 21
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 1 of 12
`
`US 6,434,157 B1
`
`OPENED IN NODE OPENED FOR MODBUS COMMAND
`PATH TYPE
`ORIGINATOR
`DATA ACCESS
`DATA MASTER (DM)
`DESTINATION
`DATA ACCESS
`DATA SLAVE (DS)
`PROGRAM MASTER (PM) ORIGINATOR
`PROGRAMMING
`PROGRAM SLAVE (PS)
`DESTINATION
`PROGRAMMING
`
`
`
`Figure I
`
`ETHERNET
`
`
`
`MODBUS PLUS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`TCP/IP
`INTERFACE
`
`BRIDGE
`8 DATA PATHS
`8 PROGRAM PATHS
`
`MODBUS PLUS
`INTERFACE
`
`18
`
`10
`
`16
`
`
`
`
`
`
`
`BP85
`
`MODBUS PLUS
`BRIDGE
`
`Figure 2
`
`ADDITIONAL
`MODBUS PLUS
`NETWORKS
`
`Page 4 of 21
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 2 of 12
`
`US 6,434,157 B1
`
`EXCEPTION CODE
`(HEXADECIMAL)
`
`
`
`
`
`MEANING
`
`06
`08
`09
`
`Busy-- NoT READY To PERFORMREQUESTED operATION
`NAK-- REOUESTED OPERATION REJECTED
`COULD NOT OPEN MODBUS PLUS PATH
`ERRORDURING MODBUS PLUS SEND
`ERRORDURING MODBUS PLUS REPLY
`
`Figure 3
`
`FUNTION CODE
`(DECIMAL)
`
`COMMAND NAME
`
`15
`16
`
`Figure 4
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 5 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Aug. 13, 2002
`Aug. 13, 2002
`
`Sheet 3 of 12
`Sheet 3 0f 12
`
`US 6,434,157 B1
`US 6,434,157 B1
`
`09
`om
`
`97
`mv
`
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`Page 6 of21
`
`Page 6 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Aug. 13, 2002
`Aug. 13, 2002
`
`Sheet 4 of 12
`Sheet 4 0f 12
`
`US 6,434,157 B1
`US 6,434,157 B1
`
`10
`10
`
`
`
`Page 7 of21
`
`Page 7 of 21
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet S of 12
`
`US 6,434,157 B1
`
`20
`
`VGA
`VIDEO
`
`PS/2
`MOUSE
`
`SERIAL
`PORT
`
`PS/2
`KEYBOARD
`
`RJ-45
`CONNECTION
`WALD
`
`34
`
`RJ-45
`1 OBASE-T
`(UTP CABLE)
`
`DB-15
`1 OBASE-5
`
`BNC
`1OBASE-2
`
`TCP/IP
`NETWORK 18
`ACTIVE
`
`36
`
`MODBUS
`PLUS
`PORT B
`
`MB PLUS
`ACTIVE
`
`
`
`
`
`ERROR
`CHANNEL B
`
`ERROR
`CHANNEL A
`
`MODBUS
`PLUS
`PORT A
`
`
`
`16
`
`38
`40
`
`42
`
`SLOT 1
`ACCESSORIES
`
`SLOT 2
`ETHERNET
`
`SLOT 3
`MODBUS PLUS
`
`Figure 7
`
`Page 8 of 21
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 6 of 12
`
`US 6,434,157 B1
`
`ONE
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`
`Page 9 of 21
`
`

`

`US. Patent
`
`Aug. 13, 2002
`
`Sheet 7 0f 12
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`US 6,434,157 B1
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`Page 10 of21
`
`Page 10 of 21
`
`

`

`U.S. Patent
`
`Aug. 13, 2002
`
`Sheet 8 of 12
`
`US 6,434,157 B1
`
`DESTINATION INDEX
`(DESTIDX)
`1 . . . 64
`
`MODBUS PLUS ROUTING PATH
`
`1. O. O. O. O. ... 64. O. O. O. O
`2 : 1 - O - O - O - 264. O. O. O
`3. 1 . O. O. O ... 3.. 64. O. O. O
`
`3. 2. 1 - O - O - 3 - 2 - 57. O. O
`
`Fig. 10
`
`
`
`BRIDGE
`PATH
`
`BRIDGE
`NODE
`ADDRESS
`1 . . .
`
`FIRST IP
`ROUTING
`BYTE
`
`1 . . . 255
`
`REQUIRED?
`
`DEFINES INDEX INTO THIS BRIDGE'S
`TCP MAPPING TABLE, AND ROUTES
`MESSAGE TO THE IP DESTINATION
`STORED IN THAT TABLE LOCATION.
`
`MB+ TABLE
`ROUTING
`BYTE
`1 . . . 249
`
`LAST
`ROUTING
`BYTE
`(NOTUSED)
`1. OPTIONAL
`IF IP DESTINATION IS ANOTHER
`TCP/IP-MB+ BRIDGE, THIS BYTE
`ROUTES MESSAGE TO THE MB+
`NODE ADDRESS IN THAT BRIDGE'S
`MB+ MAPPING TABLE.
`
`Fig. 12
`
`Page 11 of 21
`
`

`

`US. Patent
`
`Aug. 13, 2002
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`Sheet 9 0f 12
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`US 6,434,157 B1
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`US. Patent
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`Sheet 10 0f 12
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`US 6,434,157 B1
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`US. Patent
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`Aug. 13, 2002
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`Sheet 11 0f 12
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`US 6,434,157 B1
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`U.S. Patent
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`Aug. 13, 2002
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`Sheet 12 of 12
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`US 6,434,157 B1
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`Page 15 of 21
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`

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`1
`MODBUS PLUS ETHERNET BRIDGE
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`US 6,434,157 B1
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`TECHNICAL FIELD
`The present invention relates to bridges for providing a
`connection between local area networks, and in particular to
`a bridge that provides a connection between a MODBUS
`Plus network and an Ethernet network.
`
`BACKGROUND OF THE INVENTION
`Local area networks are widely used for communicating
`between data processing Systems and peripherals Such as,
`for example, those disclosed by U.S. patent application Ser.
`No. 09/036,565, filed Mar. 9, 1998, now U.S. Pat. No. 6,016,
`523 and incorporated herein by reference, and German
`Patent No. DE 196 15093 A1, filed Apr. 17, 1996, and also
`incorporated herein by reference.
`AS is well known by those skilled in the art, local area
`networks use at least one of many network protocols for
`passing data along the network. Such widely used network
`protocols include the MODBUS Plus Protocol and the
`Ethernet Transport Control Protocol/Internet Protocol (TCP/
`IP).
`The MODBUS Application Protocol used for sending
`MODBUS messages over TCP/IP. The MODBUS Applica
`tion Protocol (MBAP), is a layer-7 protocol providing
`peer-to-peer communication between Programmable Logic
`Controllers and other host-based nodes on a local area
`network. Collectively, these nodes implement all or part of
`a control application widely used for industrial applications
`in the automotive, tire and rubber, food and beverage, and
`utilities industries to name a few.
`MODBUS protocol transactions are typical request
`response message pairs. MODBUS requests contain func
`tion codes representing Several classes of Service including
`data access, online programming, and program download
`and upload classes. MODBUS responses can be acknowl
`edgments with and without data, or non-acknowledgments
`with error information. The MODBUS protocol is described
`in a reference manual entitled MODBUS Protocol Reference
`Guide, publication PI-MBUS-300, incorporated herein by
`reference.
`Because of the widespread use of MODBUS Plus and
`TCP/IP Ethernet networks, there is a need to have these
`networks communicate with each other. To the knowledge of
`the inventors, no bridges are available for facilitating Such
`communication path(s). Accordingly, the present invention
`Satisfies this need.
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`SUMMARY OF THE INVENTION
`The inventive bridge disclosed herein provides a trans
`parent multipath connection between Ethernet host applica
`tions and a MODBUS Plus industrial network. The bridge
`functions as an addressable node on each network, manag
`ing the Ethernet and MODBUS Plus protocols and translat
`ing messages between the network applications in both
`directions.
`Ethernet hosts can establish connections to the bridge and
`send messages intended for MODBUS Plus nodes. The
`bridge accepts the messages, creates internal paths for the
`MODBUS Plus transactions, waits for the MODBUS Plus
`token frame, and forwards the messages to the destination
`nodes. It receives the data responses from the MODBUS
`Plus nodes, returns them to the Ethernet hosts, and closes the
`paths.
`65
`Messages sent to the bridge on either Ethernet or MOD
`BUS Plus contain an embedded MODBUS message, con
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`2
`Sisting of a function code and additional information Such as
`register addresses and data. The bridge uses the MODBUS
`function code to determine the type of internal path required
`for the transaction, and opens a path if one is available. If a
`path is not available, a MODBUS error code (exception
`code) is returned by the bridge to the requesting node.
`The bridge provides MODBUS Data Master, Data Slave,
`Program Master and Program Slave paths as defined by the
`MODBUS function codes in the messages. In one
`embodiment, the bridge Supports up to eight concurrent Data
`paths and eight concurrent Program paths. Moreover, the
`bridge supports full five-byte MODBUS Plus routing,
`enabling transactions through MODICON BP85 MODBUS
`Plus bridges to MODBUS Plus nodes on up to three net
`works beyond the Ethernet bridge.
`The bridge maintains two internal mapping tables that
`provide address mapping between Internet Protocol
`addresses (i.e., 255.255.255.255) and MODBUS Plus path
`addresses (i.e., 64.64.64.64.64). The user can define the
`mapping at a local keyboard and monitor connection, using
`a configuration utility that is Stored in the bridge. Mapping
`tables can also be downloaded by Hypertext Transfer Pro
`tocol (HTTP) from the Ethernet host to the bridge. If neither
`method is used, the bridge provides default mapping tables.
`The user can assign the bridge's Internet Protocol (IP)
`address through a Bootstrap Protocol (BOOTP) server using
`the bridge's Media Access Control (MAC) address, or
`locally by means of the bridge's configuration utility. The
`bridge’s MODBUS Plus address is assigned in hardware
`switches on the bridge’s MODBUS Plus circuit board.
`The bridge can be mounted on a vertical panel or hori
`Zontal shelf. Its rear panel has connectors for the networks
`and for operating power. Also, light emitting diode (LED)
`indicators are provided for power, Ethernet communication,
`and MODBUS Plus communication status.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a table summarizing the four possible types of
`MODBUS Plus paths supported by the present invention;
`FIG. 2 is a block diagram of a bridge in accordance with
`the present invention connected between an Ethernet net
`work and a MODBUS Plus network;
`FIG. 3 is a table summarizing the MODBUS function
`codes which open Data Master and Data Slave paths;
`FIG. 4 is a table summarizing the MODBUS exception
`codes that may be returned by the present invention to a
`node originating a message;
`FIG. 5 is a simplified block diagram of the bridge of FIG.
`2,
`FIG. 6 is an elevated rear view of a bridge in accordance
`with the block diagram of FIG. 5 having a connector panel;
`FIG. 7 is an elevated view of the connectors provided by
`the connector panel of FIG. 6;
`FIG. 8 is a simplified perspective side view of an Ethernet
`circuit board within the bridge of FIG. 6;
`FIG. 9 depicts a menu provided by the bridge of FIG. 5
`upon execution of a configuration program;
`FIG. 10 illustrates, for the bridge of FIG. 5, default
`MODBUS Plus routing paths for Destination Indexes;
`FIG. 11 depicts an example of the bridge's default map
`ping with one custom entry made by a user;
`FIG. 12 depicts a five-byte routing path field within a
`message received by the bridge of FIG. 5 from a MODBUS
`Plus node;
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`Page 16 of 21
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`US 6,434,157 B1
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`3
`FIG. 13 shows the mapping of a message between two
`MODBUS Plus nodes via a pair of Ethernet bridges depicted
`in FIG. 5;
`FIG. 14 illustrates an example of a typical default TCP
`mapping, with one custom routing entry made by the user;
`FIG. 15 depicts a MODBUS Application Protocol Header
`having four field comprising a transaction ID, protocol type,
`message length, and destination ID.
`
`4
`Central Processing Unit (CPU) circuit board 20 with
`memory, and a backplane 22.
`The bridge housing 12 preferably consists of sheet metal
`and is wall mountable. The circuit boards are mounted
`within the bridge 10 in IBM style board guides (not shown).
`All connectors are mounted to the Side of the housing. They
`include three Ethernet 10BASE connectors, two MODBUS
`Plus connectors, a keyboard plug, a Video plug, a mouse
`plug, and a power cord plug.
`The above listed circuit boards for the bridge 10 prefer
`ably consist of off the shelf components. In an embodiment,
`the CPU circuit board 20 preferably contains a 486DX 100
`Mhz. CPU, or better, on board keyboard interface, and a local
`VGA display controller (MB display memory). In addition,
`the Ethernet circuit board 18 consists of a standard ISA bus
`Ethernet board with a 10BASE Tunshielded connector to
`provide Ethernet connectivity. Moreover, the Modbus Plus
`circuit board 16 consists of a SA85-002 board by Schneider
`Automation Incorporated. Further, power for the boards is
`Supplied by an open frame 60 watt Single output Switching
`power Supply 14.
`In an alternative embodiment, the bridge 10 consists of a
`conventional personal computer having an Ethernet circuit
`board and a MODBUS Plus circuit board operably attached
`thereto.
`The MODBUS Plus node address for the Modbus circuit
`board 16 preferably is set before installing the bridge 10 on
`the networks. The address is set by Switches (not shown) on
`the MODBUS Plus circuit board 16. The MODBUS Plus
`node should have a unique address on the network with a
`default address of 1, but can be set from 1 to 64.
`Likewise, the type of physical connection used to connect
`the bridge to the Ethernet should be set. The type of physical
`connection is Set by internal Ethernet connector jumper JP2
`on the Ethernet circuit board 18 to define the type of physical
`connection. Preferably, as stated above, the bridge 10 pro
`vides three connectors comprising: connector 22 for an
`IEEE 802.3 10Base-T unshielded twisted pair cable (UTP
`RJ45); connector 24 for an IEEE 802.3 10Base-5 thick cable
`(AIDB-155); and connector 26 for an IEEE 802.3 10Base-2
`thin cable (BNC). Likewise, the jumper JP2 has two posi
`tions wherein the first position enables both the RJ-45 and
`the BNC connectors 22, 26 and the second position enables
`the AUI connector 24.
`If the bridge 10 is being installed at a site that must meet
`CE requirements, and the 10Base-T (RJ-45) connector 22 is
`being used, a ferrite bead should be installed on the Ethernet
`cable at the RJ-45 connector. For example, ferrite bead part
`number 28A2029-0A0 from Steward in Livingston,
`Scotland, UK.
`The bridge 10 can be physically installed on a vertical
`wall panel or a horizontal Shelf using conventional mounting
`brackets. However, clearance should be provided for venti
`lation and access to the bridge's rear panel connectors and
`indicators.
`The power Supply 14 is connected to a power input
`providing either about 110 or 220 V ac. When the power
`Supply 14 is enabled to Supply power to the board Set within
`the bridge housing 12 by toggling Switch 30, light emitting
`diode 32 (LED) is illuminated to show that power is applied
`to the bridge 10.
`Ethernet and MODBUS LEDs are also provided for
`verifying the operation of the bridge 10. In particular, the
`Ethernet board 18 has an indicator 34 for showing a valid
`connection between the board's RJ-45 (UTP) jack and the
`network. The Ethernet board also has another indicator 36
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`DETAILED DESCRIPTION
`While this invention is susceptible of embodiments in
`many different forms, there is shown in the drawings and
`will herein be described in detail preferred embodiments of
`the invention with the understanding that the present dis
`closure is to be considered as an exemplification of the
`principles of the invention and is not intended to limit the
`broad aspect of the invention to the embodiments illustrated.
`AS known by those having skill in the art, two types of
`messages can be initiated to MODBUS Plus nodes using
`MODBUS commands. Programming messages are used for
`logging into a node and controlling it, as in load/record/
`Verify operations. Data acceSS messages are used to read or
`write data at the node, or to get Statistics from the node.
`When a message transaction is initiated, a logical path is
`established between the originating node and the destination
`node. The path is maintained until the transaction is com
`pleted. The type of path that is Set in each device is
`determined by the MODBUS command embedded in the
`meSSage.
`FIG. 1 summarizes the four possible types of MODBUS
`Plus paths, wherein the present invention Supports each type
`comprising: Data Master (DM), Data Slave (DS), Program
`Master (PM), and Program Slave (PS).
`An embodiment of the present invention shown in FIG. 2
`has been built that Supports up to eight paths for each type
`of path shown in FIG.1. In this embodiment, the maximum
`amount of concurrent TCP/IP connections available is
`between 8 and 16, depending on the usage of paths in host
`applications. For example, up to 16 data connections can be
`active between TCP/IP hosts and MODBUS Plus nodes (a
`maximum of 8 active DM paths and 8 active DS paths). Up
`to 16 programming paths can be active (8 PM and 8 PS).
`If MODSOFT software is being used, it sets both a PM
`45
`and a DM path in the bridge for each active connection it
`maintains to a MODBUS Plus destination node. MODSOFT
`could be running on a single host, or simultaneously on
`multiple hosts. Thus, up to eight TCP/IP connections can be
`maintained with Modsoft running on one to eight hosts.
`FIG. 3 Summarizes the MODBUS function codes which
`open DM and DS paths in the respective nodes. Devices
`which use the MODBUS protocol accept incoming requests
`