DLMS COSEM communication protocol

Supported device types and versions
Communication line configuration
Station configuration
Station parameters
Settings of transmission parameters
I/O tag configuration
I/O tag address
Literature
Changes and modifications
Document revisions

Supported device types and versions

This protocol implements serial communication with the devices (energy & water metering) according to the DLMS/COSEM standard. It can use binary HDLC protocol, the TCP/UDP Wrapper (used for communication via TCP/IP), or the Gateway protocol. Gateway protocol is used if there is a so-called Gateway device between the SCADA system and the device. The Gateway is a device connected to a network with a SCADA system and to one/more networks with energy meters (it does not have to be an Ethernet network, but e.g. RS-485 or power lines).

Two modes of addressing I/O tags are supported:

• "Short Name (SN) referencing" using 16-bit object addresses
• "Logical Name (LN) referencing" using 6-byte OBIS codes

Communication was tested with the following devices:

• EMH LZQJ (SN referencing)
• Landis ZMD400 (SN referencing)
• Iskraemeco Iskra MT880-M (LN referencing)
• ADDAX NP73E.2-18-1 (LN referencing)
• Iskraemeco AC750-G3C2 gateway  + Iskraemeco AM550-ED1.11, AM550-TD2.12 electrometers (LN referencing, Gateway mode)
• Iskraemeco AC750-G3C2 gateway + Iskraemeco AM550-ED1.11, AM550-TD2.12 electrometers (LN referencing, Wrapper mode, IPv6 communication)

The protocol supports time synchronization, the period is configured in the station configuration dialog.

Communication line configuration

• Supported line categories: Serial, SerialOverUDP Device Redundant, TCP/IP-TCP, TCP/IP-TCP Redundant, MOXA IP Serial Library, RFC2217 Client, MODEM.
• For TCP/UDP communication using TCP/UDP Wrapper, TCP/UDP ports 4059 are reserved.

Station configuration

• Communication protocol "DLMS/COSEM".

The station address (DLMS Server HDLC/MAC Address) consists of two parts: Upper MAC Address and Lower MAC Address. Each of them is in the range from 0 to 16383 (3FFFH).

As per a specification, DLMS UA 1000-2 Ed. 7.0 (Green Book) represents:

• Upper MAC Address is used for Logical Device addressing, i.e. separately addressable entity within the physical device.
• Lower MAC Address is used for Physical Device addressing, i.e. multi-drop address on the line.

Upper MAC Address is required. An implicit value, which is set when the station address is missing, is a reserved address Upper MAC Address = 1 (Management Logical Device).

In ordinary situations, when the physical device is identical with the logical one (one physical device = one logical device), this address does not need to be changed. If the physical device integrates more logical devices, you should monitor content or "0-0:41.0.0" register of "SAP assignment" class (class_id=17, attribute 2 "SAP_assignment_list") in the "DLMS SN Object List" dialog box. This dialog box shows the list of logical devices that are integrated in a physical one.

This is the example of a value representation of the "SAP_assignment_list" attribute of the "SAP assignment" class in the device which contains one logical device with Upper MAC Address 16.
See also the protocol parameter "Client MAC address" and a document "DLMS UA 1000-2 Ed. 7.0", chapter 8.4.2.3 "Reserved special HDLC addresses".

Note: for Iskraemec Iskra MT880, Upper MAC Address = 1, Lower MAC Address = 16 + last two digits of the serial number (if, for example, the serial number is 72211943, then Lower MAC Address = 16 + 43 = 59).

Note: since the station address is DLMS Server HDLC/MAC Address, it is only used when the protocol parameter "Opening mode" is set to "Direct HDLC" or "IEC Mode E" .

Station parameters

Communication station configuration dialog box - Protocol parameters tab.
They influences some optional protocol parameters. The following station protocol parameters can be set:

Table 1

10:46:05.809 30-05-2011|D|DLMS> Z Detected: '4' = 4800 Bd

Settings of transmission parameters

Example 1 - line category Serial, the communication through IR optical head.

Example 2 - line category Serial, communication through IR optical head.

Example 3 - line category Serial, communication through RS232/RS485 interface.

I/O tag configuration

Possible I/O tag types: Ai, Ci, Di, TxtI, TiA, TiR.

I/O tag address

To understand the object addressing in DLMS/COSEM protocol, you should know a so-called OBIS standard according to the IEC standard 62056-61 Object Identification system (OBIS), chapter "Annex A - Code presentation".

The "Logical Name (LN) referencing" mode directly uses the OBIS address of objects.

The "Short Name (SN) referencing" mode does not use the OBIS address but a 16-bit numerical address.

The individual data entities are presented in so-called COSEM objects (Companion Specification for Energy Metering), which are the instances of COSEM classes (COSEM interface classes, COSEM IC). Individual types of COSEM classes are specified in the document "COSEM Identification System and Interface Classes, Ed. 10.0", i.e. so-called DLMS Blue Book. Each type of COSEM class has its own identification number ("class_id"). Each class has a set of attributes that have sequence numbers. The attribute facilitates the reading of a specific parameter of a data entity.
Each instance has its beginning SN address (base_name), which is also the address of the first attribute of a class. The "logical_name" is the first attribute of all COSEM classes. By reading this attribute, an OBIS address of a data entity that is presented by a specific class can be obtained. The addresses of further attributes are calculated according to this formula in the "Short Name referencing" mode:

short_name = base_name + ((attribute_index - 1) * 0x08)

The attributes can be static or dynamic depending on whether their value is static (i.e. unchanging, set by a producer or in the configuration of the device) or dynamic (changing). In the D2000 System, we recommend configuring only the dynamic attributes, as the value of the measured data entity is in dynamic attributes. If it is necessary for the interpretation of a value in a dynamic attribute (mostly the "value" attribute), other static or dynamic attributes are read automatically. See more information in the section Supported COSEM classes.

In the following tables, you can find the supported COSEM classes. The attributes that represent the value of the data entity (i.e. value that is important for a user) are marked as "Yes, the value of an entity" in the column "Support in D2000". The static attributes are read automatically and characterized as "Automatically read".

Supported COSEM classes

Historical data reading from load profiles

The reading of historical data from load profiles is performed using the instances of COSEM classes "Profile generic" (class_id = 7), i.e. by configuring an I/O tag with an attribute 2 ("buffer"). This I/O tag always contains an invalid value in D2000 System, however, it enables reading a buffer of a specific instance of COSEM class "Profile generic".

Data about objects that are accessible by the reading of attribute "capture_objects" are stored in the buffer. D2000 System automatically searches for I/O tags that match the objects from attribute "capture_objects" (by their address parameters). The objects are searched by parameters "logical_name", "class_id", and "attribute_index".

The TELL command GETOLDVAL or ESL action GETOLDVAL start the reading of all the configured load profiles on the station. The time interval with data is always read from the load profile according to the parameters of the TELL command or ESL action.

Example: I/O tag with address::

• class_id = 7
• attribute_index = 2
• logical_name = 1-0:P.1.0

After a tell command GETOLDVAL B.ELMER_125 "06-07-2020 00:00:00" "06-07-2020 01:00:00", the KOM process queries a list of objects in a profile (by reading attribute 3):

09:44:39.558 06-07-2020|D|DLMS> Composing getRequest for LN ClassID=0007 InstanceID=1-0:P.1.0 AttributeId 3, InvokeID 65

and displays a list of received objects:

09:44:40.710 06-07-2020|D|DLMS> Received capture_objects attribute for I/O tag 'M.ELMERY_T125_1_25_PROFILE' (class_id=7, logical_name=1-0:P.1.0, attribute_index=3) are:
09:44:40.710 06-07-2020|D|DLMS> 1. logical_name=1-0:1.5.0, class_id=4, attribute_index=2
09:44:40.710 06-07-2020|D|DLMS> 2. logical_name=1-0:2.5.0, class_id=4, attribute_index=2
09:44:40.710 06-07-2020|D|DLMS> 3. logical_name=1-0:32.7.0, class_id=3, attribute_index=2
09:44:40.711 06-07-2020|D|DLMS> 4. logical_name=1-0:3.5.0, class_id=4, attribute_index=2

this reading is performed only once and the result is cached. Subsequently, data blocks containing historical values are read:

09:44:42.924 06-07-2020|D|DLMS> Block 1 complete, reading next
09:44:42.925 06-07-2020|D|DLMS> Composing Get-Request-Next for block-number 2
..
09:44:51.203 06-07-2020|D|DLMS> Get-Data-Block-Result: raw-data [0], length 88: 
09:44:51.203 06-07-2020|D|DLMS> Last Block complete, going to parse 1614 bytes

The values are parsed and assigned to the I/O tags. If the  I/O tag with the required address does not exist, a warning is displayed:

09:44:51.205 06-07-2020|D|DLMS> > Old value for I/O tag 'M.ELMERY_T125_1_25_APm_15p', (double_long_unsigned) 992660, Re=99266, Tm=06-07-2020 00:00:00 Local
09:44:51.205 06-07-2020|D|DLMS> > Old value for I/O tag 'M.ELMERY_T125_1_25_APm_15m', (double_long_unsigned) 0, Re=0, Tm=06-07-2020 00:00:00 Local
09:44:51.205 06-07-2020|W|DLMS> Cannot find I/O tag logical_name=1-0:32.7.0, class_id=3, attribute_index=2 to assign profile data!
09:44:51.205 06-07-2020|W|DLMS> Cannot find I/O tag logical_name=1-0:3.5.0, class_id=4, attribute_index=2 to assign profile data!

Note: it is necessary to configure a non-zero delay in the time parameters of the station, otherwise the reading of profiles will never get to the run (periodic reading has a higher priority). If there are several stations on the line, the delay must be higher than the duration of the periodic reading of the values of all the stations.

Supported value types of class attributes

I/O tag address - configuration dialog box

The following picture shows a configuration dialog box of the I/O tag address.

Example for Short Name (SN) referencing:

Example for Logical Name (LN) referencing:

The meaning of the parameters in the dialog box:

DLMS Object List dialog box

If these conditions are fulfilled - the device is connected to D2000 System, a communication station exists and the device communicates, you can define the parameters of the I/O tag address by the selection of the object from the list of all objects on the device. A list of objects is queried from the device:

• in SN referencing mode: from a special class "Association SN" with predefined address base_name 0xFA00
• in LN referencing mode: from a special class "Association LN" with predefined address logical_name 0.0.40.0.0.255

There is no need to configure any other I/O tags, just click on the Browse button.

The first reading of the list takes up to several minutes depending on the baud rate. The window displays the information "Waiting for data...".

After data is read, the list of objects and their descriptions will show in the window:

You can find the following information in the list:

• each row represents one instance of COSEM class,
• the OBIS address of the object follows the icon of class,
• then there is the information about the SN address (base_name) of a particular instance of COSEM class and about its type (class_id and version),
• COSEM classes, which are supported in the D2000 System, can be expanded by clicking on the symbol (+).

When expanding a specific instance of the COSEM class, the supported attributes of the class will be displayed:

The information about attribute includes:

• attribute index (attribute_index) - a sequential number of the attribute, it is displayed next to the icon,
• attribute name (e.g. logical_name, value, scaler_unit, time_zone ...),
• static or dynamic attribute.

There can be an "expand" symbol (+) near the icon. When opening it and clicking on the "Attribute value=" row, the current value of the attribute will be retrieved from the device:

This feature enables fast browsing of the attributes of all supported COSEM classes. The dialog window works as both "Object List" and "Value Browser".

The bottom part of the dialog box contains these check-boxes:

• Show hexadecimal - shows all the addresses of base_name classes as hexadecimal numbers or decimal ones.
• Show inactive objects
• Show unsupported classes - enables to display the instances of unsupported COSEM classes.

To close the dialog box without any changes, click the Cancel button.

To insert the addressing parameters of the attribute of an instance into the address of I/O tag, double-click on the particular row. This closes the "DLMS SN Object List" dialog and the parameters of the I/O tag will be configured based on the selection.

OBIS address specification

The definition of OBIS address according to IEC 62056-61 is following:

• Value group A defines the energy type (0=abstract objects, 1=electricity, 7=gas),
• Value group B defines a channel number,
• Value group C defines a measured physical value,
• Value group D defines a type of processing,
• Value group E defines further processing or classification according to the algorithm,
• Value group F defines the storage of processed historical data.

Value group A up to F represents a positive number in the range 0 up to 255.

For Value group C and D you can enter also the character values:

• character 'C' represents 96,
• character 'F' represents 97,
• character 'L' represents 98,
• character 'P' represents 99.

The address is written in  text format:

A-B:C.D.E*F

Value groups C, D, and E must always contain the value. Other unspecified values will be set to zero (0).

For more information see "List of standard OBIS codes and COSEM objects" on http://www.dlms.com, the document "List of standardized OBIS codes, DLMS UA, V2.3, (c) Copyright 1997-2005 DLMS User Association".

Literature

• DLMS User Association, COSEM Architecture and Protocols, Seventh Edition, (c) Copyright 1997-2009 DLMS User Association (Green book).
• DLMS User Association, COSEM Identification System and Interface Classes, Ed. 10.0, (c) Copyright 1997-2010 DLMS User Association (Blue book).
• International Standard IEC 62056-21, Direct Data Local Exchange, First edition 2002-05.
• International Standard IEC 62056-61, Object Identification System (OBIS), Second edition 2006-11.
• List of standardized OBIS codes, DLMS UA, V2.3, (c) Copyright 1997-2005 DLMS User Association.

Changes and modifications

-

Document revisions

• Ver. 1.0 - May 30, 2011 - Document created.
• Ver. 1.1 - January 30, 2019 - Support for LN referencing.
• Ver. 1.2 - November 11, 2021 - Support for TCP/UDP Wrapper and Gateway protocol.