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  • Electrical network protection

    Modbus communication

    Users manual06/2008

    Sepam series 80

  • SEPED303002EN - 06/2008

    Safety instructions

    Safety symbols and messagesRead these instructions carefully and look at the equipment to become familiar with the device before trying to install, operate, service or maintain it. The following special messages may appear throughout this bulletin or on the equipment to warn of potential hazards or to call attention to information that clarifies or simplifies a procedure.

    Risk of electric shockThe addition of either symbol to a Danger or Warning safety label on a device indicates that an electrical hazard exists, which will result in death or personal injury if the instructions are not followed.

    ANSI symbol. IEC symbol.

    Safety alertThis is the safety alert symbol. It is used to alert you to potential personal injury hazards and prompt you to consult the manual. Obey all safety instructions that follow this symbol in the manual to avoid possible injury or death.

    Safety messages

    DANGERDANGER indicates an imminently hazardous situation which, if not avoided, will result in death, serious injury or property damage.

    WARNINGWARNING indicates a potentially hazardous situation which, if not avoided, could result in death, serious injury or property damage.

    CAUTIONCAUTION indicates a potentially hazardous situation which, if not avoided, could result in minor or moderate injury or property damage.

    Important notesRestricted liabilityElectrical equipment should be serviced and maintained only by qualified personnel. No responsibility is assumed by Schneider Electric for any consequences arising out of the use of this manual. This document is not intended as an instruction manual for untrained persons.

    Device operationThe user is responsible for checking that the rated characteristics of the device are suitable for its application. The user is responsible for reading and following the devices operating and installation instructions before attempting to commission or maintain it. Failure to follow these instructions can affect device operation and constitute a hazard for people and property.

    Protective groundingThe user is responsible for compliance with all the existing international and national electrical codes concerning protective grounding of any device.

  • Modbus communication Content


    Presentation 2

    Managing the Modbus protocol 3

    Configuring the communication interfaces 4

    Commissioning and diagnosis 6

    Data addresses and coding 8

    Addresses in direct-access mode 10

    Time-setting and synchronization 28

    Time-tagged events 30

    Transferring records 32

    Access to remote settings 36

    Customized table 38

    Security 40

    Reading Sepam identification 41

    Appendix 1. Modbus protocol 42

    Appendix 2. Function settings 46

    1SEPED303002EN - 06/2008

  • 1

    Modbus communication Presentation





    Modbus communication allows Sepam to be connected to a supervisor or any other device with a master Modbus communication channel.Sepam is always a slave station.Sepam series 80 has two identical and independent communication ports, COM1 and COM2.

    Sepam is connected to a Modbus communication network via a communication interface.There is a choice of two types of communication interface:b communication interfaces to connect Sepam to a single network:v ACE949-2, for connection to a 2-wire RS 485 networkv ACE959, for connection to a 4-wire RS 485 networkv ACE937, for connection to a fiber-optic star networkb communication interfaces to connect Sepam to two networks:v ACE969TP-2, for connection to:- one 2-wire RS 485 Modbus S-LAN supervision communication network- one 2-wire RS 485 E-LAN engineering communication networkv ACE969FO-2, for connection to:- one fiber-optic Modbus S-LAN supervision communication network- one 2-wire RS 485 E-LAN engineering communication network.

    Access Sepam dataData availableModbus communication provides access to many different functions, including:b reading of metering and diagnosis informationb reading of status conditions and remote indicationsb transfer of time-tagged eventsb transfer of disturbance-recording datab viewing of protection settingsb reading of Sepam configuration and identificationb remote control of the analog outputb time-setting and synchronization.The actual list depends on the application, the type of Sepam and the enabled functions.

    Modbus communication also offers a number of additional functions (when enabled):b transmission of remote controlsb modification of protection settings.A password may be set up to protect access to these two functions.

    Access modesDepending on the data, two access modes are used:b direct access - the data may be accessed directly in a single read or write operationb indirect access - access requires a number of read and write operations, using a protocol that is specific to the data accessed.

    Customized tableWith Sepam series 80, it is possible to set up for each Modbus port a customized sub-group of data for quick reading of the most significant information on the user application.

    Compatibility with Sepam 2000Even though Sepam series 80 offers many additional functions, it remains compatible with Sepam 2000 addresses and formats for most information.

    Sepam series 80 - two ports for communication and remote operation by SFT2841.

    2 SEPED303002EN - 06/2008

  • Modbus communication Managing the Modbus protocol


    Protocol operationModbus is used to exchange information between a master and one or more slave units, identified by a number. It implements request-reply dialog, where requests are always initiated by the master. Modbus exists in ASCII and binary (RTU mode) formats.

    Data is exchanged in the form of 16-bit words (also called registers) or simply bits. Each piece of information (bit or register) has a 16-bit address.

    A detailed description of the protocol is provided in the appendix. It may also be found at

    Modbus functions The Modbus protocol used by Sepam series 80 is a compatible sub-group of the RTU Modbus protocol.The functions listed below are handled by Sepam series 80:b basic functions (data access):v function 1: reading of n output or internal bitsv function 2: reading of n input bitsv function 3: reading of n output or internal wordsv function 4: reading of n input wordsv function 5: writing of 1 bitv function 7: high-speed reading of 8 bitsv function 15: writing of n bitsv function 16: writing of n words.b communication-management functions:v function 8: Modbus diagnosisv function 11: reading of Modbus event counterv function 43: sub-function 14: reading of identification.b enhanced functions:v function 102: secure access.

    The following exception codes are supported:b 1: unknown function codeb 2: incorrect addressb 3: incorrect datab 4: not ready (cannot process request)b 7: not acknowledged (remote reading and setting in particular).

    Multi-master operationWhen Sepam units are connected via a gateway to a multiple-access network (Ethernet, Modbus+, etc.), a number of masters may address the same unit via the same communication port.The serial line Modbus protocol cannot manage this type of architecture. The network designer is responsible for avoiding collisions.b For direct-access data, in general, no particular precautions must be taken.b For indirect-access data, Sepam provides two exchange zones on each port, making possible two simultaneous, independent accesses by two different masters.

    PerformanceThe typical response time (time between the end of request reception and sending the reply) is less than 10 milliseconds for 90% of exchanges. It may occasionally be longer, but not exceed 150 ms.In indirect mode, the time needed between the request (or an acknowledgment) and the availability of the corresponding data is linked to the Sepam low-priority cycle time and may vary from a few dozen to several hundred milliseconds.

    3SEPED303002EN - 06/2008

  • 1

    Modbus communication Configuring the communication interfaces




    Access to configuration parametersThe Sepam communication interfaces must be configured using SFT2841 software.The configuration parameters can be accessed from the Communication configuration window in the SFT2841 software.To access this window:b open the Sepam configuration window in SFT2841b select the communication port you are going to configure, by checking the COM1 or COM2 boxb click on the relevant button : the Communication configuration window appearsb select the type of interface used: ACE949/ACE959/ACE937, ACE969TP or ACE969FOb select the Modbus communication protocol.

    The configuration parameters will vary depending on the communication interface selected: ACE949/ACE959/ACE937, ACE969TP or ACE969FO. The table below specifies the parameters to be configured depending on the communication interface chosen.

    SFT2841: Sepam configuration screen.

    Parameters to be configured ACE949ACE959ACE937

    ACE969TP ACE969FO

    Physical layer parameters b b bFiber-optic parameters bAdvanced Modbus parameters b b bE-LAN parameters b b




    SFT2841: communication configuration window for ACE949.

    Configuring the physical layer of the Modbus portAsynchronous serial transmission is used with the following character format:b 1 start bitb 8 data bitsb 1 stop bitb parity according to parameter setting.The number of stop bits is always fixed at 1.If a configuration with parity has been selected, each character will contain 11 bits: 1 start bit + 8 data bits + 1 parity bit + 1 stop bit.If a no parity configur


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