IEC 60870-5-104 communication protocol

Supported device types and versions
Communication partners
Communication line configuration
Communication station configuration
TELL commands
I/O tag configuration
Literature
Document revisions

Supported device types and versions

The protocol (known also as IEC 870-5-104 or IEC-104) allows reading and writing data, operating on the basis of TCP network communication. Implementation is, according to the IEC 60870-5-104 standard, as follows:

• Originator ASDU address is 1 byte, it is defined as the line number.
• ASDU address is 2 bytes, it is defined as the station address. ASDU addresses of all stations on one line must be different.
• Cause of transmission is 2 bytes (contains also Originator ASDU address).
• Information object address is 3 bytes, it is defined as an I/O tag address.
• The following ASDU types are implemented in the monitoring course (from controlled station to the D2000 system and also vice-versa in balanced mode):

Table 1

Note: Single bits of the byte, which informs us on quality (SIQ for ASDU 1,2,30; DIQ for ASDU 3,4,31; QDS for 5..14,20,32..36) are mapped into the A (0.bit), B (1.bit) .. H (7.bit) flags except the bits that are directly set by the value of the variable ( SCO bit 0, DCO and RCS bits 0-1). After receiving the answer (a positive/negative one), the A .. H flags are set according to bits of "status" byte.

For example:
for ASDU 4: A=DPI bit 0, B=DPI bit 1, C=0, D=0, E=BL bit, F=SB bit, G=NT bit, H=IV bit.
for ASDU 16: A .. E Sequence number bits 0..4, F=CY bit, G=CA bit, H=IV bit.

Moreover:

• if a bit is set to IV (Invalid), the value state will be Invalid
• if some of the bits are set to NT (Not topical), SB (Substituted), BL (Blocked), OV (Overflow), CA (Counter adjusted), CY (Counter overflow) for corresponding ASDU types, the value state will be Weak.

* - T-bit of the value of these ASDU types is in the I flag, a number within -64 .. +63 is in a variable of Ci/Ai type.
** - ASDU 17 and 38: SEP byte is in the flags A (0.bit), B (1.bit) .. H (7.bit), the following 2 bytes (CP16Time2a) are in a variable of Ci/Ai type as a positive number (0-60 000) or they are in a variable of TiR type as a relative time (0-60 seconds).

*** - ASDU 18, 39 and 40: SPE(ASDU 18,39) byte respectively OCI (ASDU 40) byte is in the flags I (0.bit), J (1.bit) .. P (7.bit), QDP byte is in the flags A (0.bit), B (1.bit) .. H (7.bit), the following 2 bytes (CP16Time2a) are in a variable of Ci/Ai type as a positive number (0-60 000) or they are in a variable of TiR type as a relative time.

The following ASDU types are implemented in the control course (from D2000 system to controlled station and also vice-versa in balanced mode):

Table 2

To set the bits of "status" byte (SCO for ASDU 45,58; DCO for ASDU 46,59; RCO for ASDU 47,60; QOS for ASDU 48..50,61..63), the flags A (0.bit), B (1.bit) .. H (7.bit) are used, except the bits, which are directly set by the variable value (SCO bit 0, DCO and RCS bits 0-1). Having received a response (positive/negative), the A .. H flags are set according to the bits of the "status" byte.

When sending commands (ASDU 45-64), the value of 6 [Activation] is sent as a CauseOfTransmission. The expected response from the controlled station depends on the Command Confirm parameter. There are the following possibilities:
- writing is successful if the packet with RSN confirming the SSN packet with the write command
- writing is finished, if there is a response with CauseOfTransmission=7 [Activation Confirmation] and/or with 10 [Activation Termination]. Success/failure depends on the setting of the P/N bit in CauseOfTransmission.

**** - ASDU 250 can be used for communication with Ipesoft 870-5-104 Server. The command will ask for historical values (within specified interval) from the server, which will arrive as ASDU 251 (or newer ASDU 249 that use 64-bit values for improved precision, if the protocol parameter D2H64 is enabled on the server). The reading of the archive values can be executed by means of the GETOLDVAL command with the parameter containing the name of the I/O tag or station (in this case, the values of all I/O tag are read gradually, i.e. reading of the next tag starts after the reading of current tag is done).
Response for ASDU 250 is again ASDU 250 (with CauseOfTransmission=7) and with the return code:

• 0 - the successful start of reading the history
• 1 - the history for the required tag doesn't exist
• 2 - the history for the required tag is not available (the archive does not run)

Next (is the return code was 00) the ASDU 251 with archive data will be sent and the termination ASDU 250 with CauseOfTransmission=10.

Establishing a connection:

The D2000 KOM process is connecting to the TCP port and sends a StartDT Act U-frame, then a StartDT Con U-frame is expected as a reply.

For all the stations with a defined synchronization (see the article below), an ASDU type 103 [Clock synchronisation command] with CauseOfTransmission=6 [Activation] is sent, and a reply (depending on the Command Confirm parameter) is expected.

Then a sequence of 0 up to N I-frames with ASDU 100 [Interrogation Command] and ASDU 101 [Counter Interrogation Command] is sent, both with CauseOfTransmission=6 [Activation]. The I-frames are sent for each station with at least one input I/O tag (i.e. Ai, Di, Qi, Ci). The expected response (in any order) is:

• reception of frames with ASDU 100 [Interrogation Command] and with CauseOfTransmission=7 or 10 (depending on the Command Confirm parameter)
• reception of frames with ASDU 101 [Counter Interrogation Command] and with CauseOfTransmission=7 or 10 (depending on the Command Confirm parameter)
• reception of current values of all I/O tags.

The other side can also send frames with ASDU TypeIdentificator=100 and CauseOfTransmission=10 [Activation Termination]. However, the D2000 KOM process does not consider it to be an error if such no frames are received. The order of sending ASDU 100 and 101 as well as disabling their sending is defined by the Order of IC and Order of Counter IC parameters.

Clock synchronisation: Sending ASDU type 103 [Clock synchronisation command] is performed during initialization (after sending StartDT and before sending Interrogation Command). The synchronization is sent for the stations, with the Enable parameter checked in the Time parameters tab. ASDU type 103 is sent regularly with a defined period.

Forced disconnection: If all stations on the line are in the simulation mode or the communication is stopped for them, the line will be disconnected (the communication socket will be closed). If the simulation is disabled for at least one station and the communication is not stopped for it (the Parameters tab of Station type object), the line will be connected again (and Interrogation Command and/or Counter Interrogation Command will be sent to the active station). After enabling communication for further stations, Interrogation Command and/or Counter Interrogation Command will be sent to these stations, see the next paragraph.

Forced sending of Interrogation Command and/or Counter Interrogation Command: If a station is in the simulation mode, and the communication is not stopped for it (the Parameters tab of Station type object), the D2000 KOM process sends Interrogation Command and/or Counter Interrogation Command (see the parameters Order of IC, Order of Counter IC).

The D2000 system also supports a balanced mode. In this mode, the task of controlled and control stations is symmetrical. In this mode, the D2000 system receives commands and confirms them. The balanced mode may be used only when it is supported by the partner station. An advantage is that the D2000 system sends the current status of output I/O tags (defined as ASDU 1-40) as a reply to ASDU 100 [Interrogation Command] and 101 [Counter Interrogation Command] requests. It is still suitable to configure single-shot commands as ASDU 45 - 64; they are not repeated after re-establishing the connection.
As the protocol supports the balanced mode (partly it is a server), the rules of server protocols apply to it.
The output tags, which are configured as ASDU 1-40, do not go through the Transient status (i.e. they are considered as if in the configuration of I/O tag, Output control tab, the I/O tag output mode is set to Command). The writing is considered to be successful if there is a connection with the server at the time of writing, otherwise, the writing is unsuccessful.

Communication partners

• ABB MicroScada. Note: The value of the parameter Maximum message length in the ABB MicroScada settings must be changed from 253 similar to 230 (+/- a few bytes). Default value of the parameter causes rewriting the communication buffer and it is expressed by sending a corrupted message.
• PLC Bernecker & Rainer, protocol implementation: URAP-AUTOMATIZÁCIA s.r.o. (Ltd.)
• LFC terminals of Slovenské Elektrárne, a.s. (Inc.), protocol implementation: Energodata/ABB
• RS Unicon 4, UniControls

Communication line configuration

• Communication line category: TCP/IP-TCP or TCP/IP-TCP Redundant.
• TCP parameters - server parameters are mandatory:
  • Host: string containing at most 80 characters – server name in form of INET (name or numerical address a.b.c.d). In the case of redundant systems, multiple names/addresses separated by commas can be entered.
  • Port: TCP port number (0..65535)
  • Line number: is to be used as the Originator ASDU address (1 byte, 0-255)

Communication station configuration

• Communication protocol: IEC870-TCP.
• Station address: a number within the range of 0..65535 defines the ASDU address. It can be specified as a decimal number or as a hexadecimal number with a hash at the beginning (e.g. #0A).

Note 1: After saving a station in process D2000 CNF, the process D2000 KOM automatically sends ASDU 100 and ASDU 101 (Interrogation and Counter Interrogation Commands) to this station, if enabled.

Note 2: The protocol supports sending long time stamps (CP56Time2a tag) in local time or UTC time with defined offset (see the parameter Use monotonic UTC time +).

Note 3: Starting with D2000 version 7.02.004 if a TCP Redundant line category is used, the C and D flags are used in the value of communication stations for an indication of the functionality of primary (C) and secondary (D) communication paths. If these flags are set, the respective communication path is non-functional. For example, if the value of the communication station is StON and the C flag is set it means that only the secondary communication path is functional.
For lower versions of D2000 only partial detection of a broken communication path is available when using the Strict Redundancy Connection Signalisation parameter.

The Browse button opens a browsing dialogue for the station address. If the communication is functional, a dialogue with the ASDU addresses received so far is displayed. The Refresh button can be used to clear the list of received ASDU addresses.

Station protocol parameters

Table 3

Defined parameters, except for Order of IC, Order of Counter IC, and Force Slave Time, are valid for the entire line - i.e. it is enough to define them for one station on the line.

TELL commands

Table 4

Examples of configurations

Example 1: Client communicating with the server SrvA on a redundant network.

If a communication segment drops out (e.g. IPA1 failure) the client establishes a connection with the server SrvA using the address IPA2.

Example 2: Client communicating with the redundant servers SrvA, SrvB.

The client communicates both with the active and passive server, connection with the passive server continues to be open, but new values are sent by the active server only.
Note: If a symbolic name myName is used in the configuration of the IEC104 Server, it should be defined as IPA in the hosts file of the 1-st server and as IPB in the hosts file of the 2-nd server.

Example 3: Client communicating with the redundant servers SrvA, SrvB on a redundant network.

The client communicates with both servers. If one network segment drops out (e.g. IPA1 failure), the client establishes a connection with the SrvA server using the IPA2 address.

Example 4: The redundant clients ClientC, ClientD communicating with the redundant servers SrvA, SrvB on a redundant network.

The clients communicate with both servers. If one network segment drops out (e.g. IPA1 failure), the clients establish a connection with the SrvA server using the IPA2 address. After switching the active/passive statuses of the ClientC and ClientD clients, they keep communicating with the servers, however, only the active client sends commands. New values are sent by the active server.

I/O tag configuration

Possible I/O tag types: Ai, Ao, Ci, Co, Di, Dout, Qi

• I/O tag address is mapped to the Information object address, i.e. it has 3 bytes and must be within the range of 0..16777215. It can be specified as a decimal number or as a hexadecimal number with a hash at the beginning (e.g. #0A).
  The I/O tag with an address starting with %IGNORE will be ignored.
  
• Input tags must be of particular types (Ai, Ci, Di, Qi) for received ASDU, see table 1 and also table 2 in the balanced mode.
• For a particular type of output tag (Ao, Dout, Co), it is necessary to set an ASDU type, that has to be used, see table 2.
• Archive for providing historical values: if the client asks for historical values through ASDU 250, the server sends:
  1. the values of the historical value specified by this input entry field,
  2. if the input entry field is not filled, then the values of the historical value that archives the I/O tag,
  3. if the specified historical value does not exist, then the values of the I/O tag that archives the control object of the specified I/O tag,
  4. if the control object does not exist (or the archive is not available), the server returns an error.
  Specification of a historical value allows configuring e.g. sending 10-minutes averages instead of sending all changes of given I/O tag.
• If the Destination Column is configured, then the values received from the address configured at the I/O tag and above are stored in the corresponding items (e.g. objects with addresses 10, 11, 12 ... according to the number of rows of the destination structure).

Literature

Document revisions

• Ver. 1.0 – July 30th, 2003
• Ver. 1.1 – November 19th, 2003: extension of supported ASDU, new parameters
• Ver. 1.2 – March 20th, 2004: added ASDU for reading archive data
• Ver. 1.3 – June 20th, 2004: extension - redundancy support
• Ver. 1.4 – December 1st, 2004: extension - support of balanced mode
• Ver. 1.5 - December 12th, 2012 - updating, TELL commands
• Ver. 1.2 – November 16th, 2023 (support for the Destination Column)