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1MAC052634-MB D

Section 2

Modbus overview

615/620 series ANSI

7

Communication Protocol Manual

Section 2

Modbus overview

2.1

Modbus standard

Modbus is a communication protocol developed by the Modicon company in the 1970’s.
Originally it was used for communication in PLCs and RTU devices. Later on the Modbus
protocol has been used in a variety of different device applications. Today the Modbus
protocol is mainly used over serial communication networks and Ethernet.

The Modbus serial communication and the Ethernet based Modbus TCP/IP
communication in this IED follow the specifications maintained by Modbus Organization.

2.1.1

Serial communication

Modbus is a master-slave protocol when it is used over serial communication networks.
This IED implements the slave side of the protocol. Depending on the chosen physical
serial interface it is possible to build multidrop networks or point-to-point communication
connections.

There can only be one Modbus master unit on a Modbus serial network. The Modbus
master unit communicates with one Modbus slave unit at a time. Usually the master reads,
or scans, data from the slaves cyclically. The master can also write data or give commands
to the slave units. Each slave unit has a unique unit address. Thus, the master can identify
the slave with which it communicates. The Modbus standard also defines the possibility
for Master broadcast transmissions.

Modbus serial protocol uses two link modes: Modbus RTU and Modbus ASCII. Both
modes are supported by this IED.

2.1.2

Ethernet communication

Modbus communication over Ethernet TCP/IP is of client-server type. This IED operates
as a Modbus server.

Modbus TCP/IP connection is established when the Modbus client opens a TCP socket
connection to the Modbus server. The socket port 502 on the TCP/IP stack is reserved for
Modbus. If the connection request is accepted by the server, the client can start
communicating with the server unit.

IEDs can usually accept several simultaneous Modbus TCP/IP client connections even
though the number of connections is limited. It is possible to configure the IED to only
accept socket connection requests from known client IP addresses.

Modbus communication reference guides are downloadable from
Technical Resources at www.modbus.org.

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Summary of Contents for 620 Series ANSI

Page 1: ...Relion Protection and Control 615 620 series ANSI Modbus Communication Protocol Manual ...

Page 2: ......

Page 3: ...Document ID 1MAC052634 MB Issued 11 23 2010 Revision D Copyright 2010 ABB All rights reserved 615 series Product version 2 0 620 series Product version 1 0 ...

Page 4: ...osed only in accordance with the terms of such license Trademarkss ABB and Relion are registered trademarks of ABB Group All other brand or product names mentioned in this document may be trademarks or registered trademarks of their respective holders Warranty Please inquire about the terms of warranty from your nearest ABB representative ABB Inc Distribution Automation 4300 Coral Ridge Drive Cora...

Page 5: ...product failure would create a risk for harm to property or persons including but not limited to personal injuries or death shall be the sole responsibility of the person or entity applying the equipment and those so responsible are hereby requested to ensure that all measures are taken to exclude or mitigate such risks This document has been carefully checked by ABB but deviations cannot be compl...

Page 6: ... electrical equipment for use within specified voltage limits Low voltage directive 2006 95 EC This conformity is the result of tests conducted by ABB in accordance with the product standards EN 50263 and EN 60255 26 for the EMC directive and with the product standards EN 60255 6 and EN 60255 27 for the low voltage directive The IED is designed in accordance with the international standards of the...

Page 7: ...a implementation 8 Terms and definitions 8 Documentation 8 Section 3 Vendor specific implementation 9 Modbus link alternatives 9 Serial link 9 Modbus serial link parameters 9 Modbus serial diagnostic counters 10 Character framing in different serial link modes 11 TCP IP link 11 TCP IP interface configuration 12 Modbus TCP IP diagnostic counters 13 Supported function codes 14 Application functions ...

Page 8: ...25 SSR1 25 SSR2 26 SSR3 26 SSR4 27 SSR5 28 SSR6 28 Event records 29 Single event record structure 29 Single event record reading 30 Other event record registers 31 Multiple event records reading 35 Fault records 38 Fault record structure 38 Parameter setting group selection 42 Time synchronization 42 Real time clock structure 42 Writing to real time structures 42 Device information 43 ASCII charac...

Page 9: ...entrates on vendor specific implementations 1 2 Intended audience This manual addresses the communication system engineer or system integrator responsible for pre engineering and engineering for communication setup in a substation from an IED perspective The system engineer or system integrator must have a basic knowledge of communication in protection and control systems and thorough knowledge of...

Page 10: ...d The operation manual contains instructions on how to operate the IED once it has been commissioned The manual provides instructions for monitoring controlling and setting the IED The manual also describes how to identify disturbances and how to view calculated and measured power grid data to determine the cause of a fault The application manual contains application descriptions and setting guide...

Page 11: ... and conventions 1 4 1 Safety indication symbols Although warning hazards are related to personal injury it should be understood that operation of damaged equipment could under certain operational conditions result in Document revision date Product series version History A 03 28 2008 1 0 1 First release B 12 22 2008 1 1 Content updated to correspond to the product series version C 01 20 2010 2 0 C...

Page 12: ... icons for example To navigate between the options use and HMI menu paths are presented in bold for example Select Main menu Settings LHMI messages are shown in Courier font for example To save the changes in non volatile memory select Yes and press Parameter names are shown in italics for example The function can be enabled and disabled with the Operation setting Parameter values are indicated wi...

Page 13: ...s with one Modbus slave unit at a time Usually the master reads or scans data from the slaves cyclically The master can also write data or give commands to the slave units Each slave unit has a unique unit address Thus the master can identify the slave with which it communicates The Modbus standard also defines the possibility for Master broadcast transmissions Modbus serial protocol uses two link...

Page 14: ...can be accessed using command functions belonging to Modbus conformance classes 0 and 1 This means that most master systems are able to communicate with the IED 2 2 Terms and definitions Modbus data appears in different memory areas in the Modbus device The four most common areas are coils digital input input register and holding register These are also referred to as 0X 1X 3X and 4X areas respect...

Page 15: ...odbus RTU and ASCII link modes and the unit address 3 1 1 1 Modbus serial link parameters Serial link setting parameters can be accessed with PST or via the LHMI path Configuration Communication Modbus Address Each serial link can be given a separate unit address End delay The end of message delay or timeout is used only in the Modbus RTU link mode According to the Modbus standard an idle period o...

Page 16: ...l diagnostic counters can be viewed via the LHMI path Monitoring Communication Modbus Serial Counters related to the possible Modbus serial instances 1 2 have the suffixes 1 2 N The counters show complete Modbus protocol link frames and Modbus errors The serial communication drivers COM1 COM2 maintain their own counters for lower level serial communication diagnostics In a multidrop RS 485 Modbus ...

Page 17: ...at contain a proper link address All other incoming Modbus frames are discarded Transmitted Exc A N Total amount of exception responses 1 and 2 These exception responses usually reveal configuration errors on the Modbus client side Either the client uses a request function code which is not supported or the requested Modbus point s does not exist Transmitted Exc B N Total amount of exception respo...

Page 18: ...ections by registering the clients IP addresses For example if four concurrent connections are allowed and three of them are registered they are seen as Client connection 1 Client connection 3 These three registered connections are then dedicated to certain clients only and the fourth connection is available to other clients Client IP addresses There are five Modbus setting parameters for Modbus c...

Page 19: ...ains its own counters for lower level communication diagnostics Table 4 TCP IP diagnostic counters The counters and status of an instance N are reset when the client makes a TCP socket disconnection or if the TCP socket connection keep alive times out The common instance independent Modbus TCP IP diagnostic counters can be reset separately by writing the value 0 into them Counter Description Recei...

Page 20: ...registers Reads the contents of output registers 04 Read input registers Reads the contents of input registers 05 Force single coil Sets the status of a discrete output 06 Preset single register Sets the value of a holding register 08 Diagnostics Checks the communication system between the master and the slave 15 Force multiple coils Sets the status of multiple discrete outputs 16 Preset multiple ...

Page 21: ...ount The response returns the number of messages addressed to the slave or broadcast which the slave has processed since its last restart clear counters operation or power up 15 Return slave no response count The response returns the number of messages addressed to the slave for which a response neither a normal response nor an exception response has not been sent since its last restart clear coun...

Page 22: ...ese objects is always found in the Modbus database The DS column in the Modbus point list manual shows if the object resides in some data set as a default 3 3 2 Modbus data implementation The IED is internally modelled according to the IEC 61850 standard The Modbus protocol is implemented on top of this model However all features of the IEC61850 data model are not available through the Modbus inte...

Page 23: ...easurands The proprietary Modbus event buffer can be read in many different ways A master can continuously read and log change events in real time or for example read out the n latest events on demand Change detect data can be used as an alternative to the event record reading to catch fast indication data transitions between the master scans The Modbus fault record gives a summary of the captured...

Page 24: ...ted to the 4X registers map Some control bits are packed bits in the 4X control register structures The 4X control structure contains a password which has to be given before starting control operations 3 3 4 Digital input data Indication signals related to protection applications often change rapidly Thus the Modbus master might not be able to detect all changes Momentary and momentary change dete...

Page 25: ...he objects open and close bits are coded as MOM MCD bit pair entities The MCD bits reveals if the object has changed its position several times since the Modbus master last scanned it In addition the open and close bits are also coded using MOM values only among with a fault bit The fault bit is set to 1 when the object is in intermediate 00 or faulty 11 position Table 9 Bit treatment The MOM valu...

Page 26: ... or counters are located in single 16 bit registers The measurands are either unsigned or signed two s complement values while the counters are always unsigned values In some rare cases the measurands or counter values can be located in two consecutive registers thus forming a single 32 bit integer value The 32 bit value is always coded so that the high word part that means the higher 16 bits is l...

Page 27: ...oth 1 and 0 to the persistent outputs Therefore the persistent outputs have two defined levels 0 and 1 Most of the outputs in this IED are pulse outputs Control operation modes This IED supports two control models direct operate and select before operate The single point control objects in this IED are of direct operate type The double point control objects can be configured either into the direct...

Page 28: ...can be operated at a time when the 4X control structures are used Exception codes Only a few exception code alternatives exist for the write coil and write register requests in Modbus 01 illegal function 02 illegal address 03 illegal value The exception code 03 is also returned if a command operation is rejected due to the IED s other internal reasons The client can find the code for the internal ...

Page 29: ...ue 1 is written into this register Password register 1 If a password is defined the two first ASCII characters of the four character password are written into this register the first character into the higher byte and the second character into the lower byte of the register If no password is defined for the control structure this register is not checked by the IED Password register 2 If a password...

Page 30: ...an find the code for the internal rejecting reason in the SSR6 register For example the primary internal rejection reasons for control structure write operations may be that The Modbus control structure write has timed out 15 sec The client has no write authority The IED is in the local state The control operation is blocked that means already reserved by another client If a positive acknowledgeme...

Page 31: ... are several control structures they are located one after another in the Modbus 4X memory map Refer to the IED s Modbus memory map for the actual locations of control structures 3 3 7 System status registers See Modbus ANSI point list manuals for specific register locations Table 13 System status registers 3 3 7 1 SSR1 The bits in SSR1 are common for all Modbus clients The bits in SSR1 give an ov...

Page 32: ...t 5 is set to 1 if any MCD bit has been set in the Modbus memory map The bit is reset when the client reads the register Bit 6 is set to 1 to indicate the device restart The bit is reset when the client reads this register Bit Meaning 0 Device global warning 1 Device global error 2 Slot 0 X130 warning or error 3 Slot 1 X120 warning or error 4 Slot 2 X110 warning or error 5 Slot 3 X100 warning or e...

Page 33: ...ds to data category 1 bit 1 to data category 2 and so on If a bit is set to 1 some data belonging to the category in question has changed since the client last scanned the register The SSR4 bit or bits are cleared when the register is read The data category number for each Modbus data is shown in the Modbus memory map The meaning of the category number is available in a separate table If the data ...

Page 34: ...R6 register ClientCmdSEQNo Counts the client s control operations from 0000 1111 that is 0 15 and then starts over CmdState 00 No write command has ever been issued by this client 01 Command in progress 11 Response Ready Bit Meaning Data category 0 Data in category 1 changed 1 Physical inputs 1 Data in category 2 changed 1 Protection function pickup trip 2 Data in category 3 changed 1 LED Alarm 3 ...

Page 35: ...rack of where in the event buffer the different clients are reading at the moment Clients are identified either by the serial port from where the requests are issued or by the client s IP address in the TCP IP network Up to 25 different IP addresses are memorized by the IED Multiple events reading backwards compatibility The original 615 620 series event reading concept only allowed reading out on...

Page 36: ...ad events before the IED knows which internal event has been sent to this specific client during the last reading The IED then loads the next event that is the oldest unread event Address Register Values Comment 4xxxx 1 Event selection 1 4 and 1 499 Write register 4xxxx 2 Sequence Number 0 65535 4xxxx 3 Unread records left 0 499 4xxxx 4 TimeStamp Year Month High byte year low byte month 4xxxx 5 Ti...

Page 37: ...ere can be 500 event records altogether Selection code 3 Resetting the event read pointer The write selection 3 is not followed by a read operation The selection 3 means that there are no unread records in the Modbus event buffer left for the client in question that is the buffer is cleared The next new event that is logged into the Modbus event buffer becomes the first unread record for this spec...

Page 38: ... 16 bit register Event time stamp format bit 15 Event time stamp format Event time stamp source bit 14 The time stamp can be generated by the IED application accurate time or by Modbus If generated by Modbus the change values are detected by the Modbus background scan task Since there is a latency time between the value change and the time when Modbus detects the change the time stamp is not accur...

Page 39: ...address or UID The coding alternatives cannot occur simultaneously in the IED but are selected and configured at the system setup phase The default setting is Modbus address The UID code is 32 bits wide and occupies both registers The word order is high low The UID code refers to the functional design of the IED platform in which the object resides Shortly it means that the UID code is equal in al...

Page 40: ...ual Point Status of a controllable object X ACT Trip status X ACD Start Pick up status X INS INC Integer status X Register 4xxxx binary coded value Meaning xxxx xxxx xxxx xxx0 Object in OFF position xxxx xxxx xxxx xxx1 Object in ON position Register 4xxxx binary coded value Meaning xxxx xxxx xxxx xx00 Object in intermediate position changing xxxx xxxx xxxx xx01 Object in ON close position xxxx xxx...

Page 41: ...gth must thus be adjusted depending on the number of records requested The selection read operation is otherwise exactly similar to the single record read case The next records to be returned always continues from the last record in the previous read operation Register address1 1 See Modbus ANSI point list manual for specific event record structure mappings Meaning 4xxxx Higher 16 bit part of the ...

Page 42: ...ed amount of event records is always returned for reading For example if 10 event records are requested but the IED only contains five event records the last valid event record is repeated duplicated in the last five event records returned The easiest way to detect the duplication is to check the sequence number of the event records The sequence numbers remain similar to the duplicated event recor...

Page 43: ...xxx 6 TimeStamp 1 4xxxx 7 TimeStamp 1 4xxxx 8 Event Type 1 4xxxx 9 Data Object Id 1_1 4xxxx 10 Data Object Id 2_1 4xxxx 11 Data Value 1 4xxxx 12 Data Value 1 4xxxx 13 Sequence Number 2 Event record 2 4xxxx 23 Data Value 2 4xxxx 24 Sequence Number 3 Event record 3 4xxxx 34 Data Value 3 4xxxx 35 Sequence Number 4 Event record 4 4xxxx 45 Data Value 4 4xxxx 46 Sequence Number 5 Event record 5 4xxxx 56...

Page 44: ...pendently of one another read out the Modbus fault records from the IED The Modbus fault record buffer keeps track of where in the buffer the different clients are reading at the moment Clients are identified either by the serial port from where the requests are issued or by the client s IP address in the TCP IP network 3 3 9 1 Fault record structure The IED s fault record structure consists of a ...

Page 45: ...y in different types of IEDs A client can read out more Modbus registers than are actually coded in one structure when reading out the data structures The maximum read amount is 80 Modbus registers The additional trailing registers contain the Address1 1 See Modbus ANSI point list manual for specific event record structure mapping Register Values Comment 4xxxx Fault record selection 1 4 and 1 99 W...

Page 46: ...cord becomes the oldest unread The client can continue by reading out the oldest unread fault records again with the selection code 1 Selection code 1 99 A negative selection code that is a 16 bit two s complement value defines how many records backwards from the newest fault record the reading is to be moved For example the ten latest fault records can be read out at any time by first selecting 1...

Page 47: ...rValue MOD 256 An exception is the milliseconds register which contains the milliseconds 0 999 coded as such Time stamp also contains a time quality register Time quality Table 30 Information contained by the 16 bit bits 15 0 register Event time stamp format bit 15 The time stamp format can be selected with a Modbus parameter via the LHMI or the parameter setting tool Event time stamp source bit 1...

Page 48: ...e available in the Modbus memory map the IED s local time and the internal UTC time Time synchronization can be given either to the local time structure or to the UTC time structure 3 3 11 1 Real time clock structure Table 31 Modbus real time clock structure 3 3 11 2 Writing to real time structures The Modbus time synchronization can be done in several ways Over the serial interface the host s syn...

Page 49: ...en the value 2 is written the timesync registers are latched onto the IED s internal clock and the reservation of the control register is released There is an internal timeout for the clock setting The time synchronization reservation is released if the clock is not set within two minutes The client can abort the time synchronization at any time by writing 0 into the control register In that case ...

Page 50: ...card Sections 0 to 4 contain version information of the additional HW cards slots 0 4 If an additional card does not include any version information it is signalled with a minus character in the swRev field If both swRev and hwRev are signalled with signs the card in question does not exist in the IED The data within the C section is restricted to certain maximum lengths For example the user defin...

Page 51: ...I point list manual for specific event record structure mapping Register Values Comment 4xxxx TimeStamp Year Month High byte year low byte month 4xxxx 1 TimeStamp Day Hour High byte day low byte hour 4xxxx 2 TimeStamp Min Sec High byte min low byte seconds 4xxxx 3 TimeStamp Milliseconds Word milliseconds 4xxxx 4 Time Quality See Time quality table 4xxxx 5 Cause of reset 1 Power reset 2 Watchdog re...

Page 52: ...Section 3 1MAC052634 MB D Vendor specific implementation 46 615 620 series ANSI Communication Protocol Manual ...

Page 53: ...n Parity for Serial interface 1 Address 1 1 255 1 Modbus unit address on Serial interface 1 Link mode 1 1 RTU 2 ASCII 1 RTU Modbus link mode on Serial interface 1 Start delay 1 0 20 char 4 Start frame delay in chars on Serial interface 1 End delay 1 0 20 char 3 End frame delay in chars on Serial interface 1 Serial port 2 0 Not in use 1 COM 1 2 COM 2 0 Not in use COM port for Serial interface 2 Par...

Page 54: ...0 Modbus Registered Client 4 ClientIP5 000 000 000 000 Modbus Registered Client 5 CtlStructPWd1 Password for Modbus control struct 11 CtlStructPWd2 Password for Modbus control struct 2 CtlStructPWd3 Password for Modbus control struct 3 CtlStructPWd4 Password for Modbus control struct 4 CtlStructPWd5 Password for Modbus control struct 5 CtlStructPWd6 Password for Modbus control struct 6 CtlStructPW...

Page 55: ...itted Exec A N 0 2147483648 Transmitted exception responses 1 and 2 by instance N Transmitted Exec B N 0 2147483648 Transmitted exception responses 3 by instance N Status N True False Status of communication instance N Reset of diagnostic counters instance N Parameter Values range Description Received frames N1 1 N instance number 1 2 0 2147483648 Received Modbus frames by instance N Transmitted f...

Page 56: ...Section 4 1MAC052634 MB D Modbus parameters and diagnostics 50 615 620 series ANSI Communication Protocol Manual ...

Page 57: ...inally developed by Westronic The DNP3 Users Group has the ownership of the protocol and assumes responsibility for its evolution DPC Double point control DPS Double point status DS Data set EMC Electromagnetic compatibility Ethernet A standard for connecting a family of frame based computer networking technologies into a LAN HMI Human machine interface HW Hardware IEC 61850 International standard...

Page 58: ...r PLC Programmable logic controller PST Parameter Setting Tool in PCM600 RS 485 Serial link according to EIA standard RS485 RTC Real time clock RTU Remote terminal unit SCADA Supervision control and data acquisition SEC Security violation SPC Single point status of a controllable object SPS Single point status SSR1 System status register for device health SSR2 System status register for device mod...

Page 59: ......

Page 60: ...istribution Automation 4300 Coral Ridge Drive Coral Springs FL 33065 USA Phone 1 800 523 2620 Phone 1 954 752 6700 Fax 1 954 345 5329 www abb com substationautomation 1MAC052634 MB D Copyright 2010 ABB All rights reserved ...

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