zenon IEC 60870 driver

The zenon IEC 870 driver supports both IEC 60870-5-101 (serial) and IEC 60870-5-104 (TCP/IP) connections. In combination with the also available drivers for IEC 61850 and DNP3, the IEC870 driver facilitates flexible substation integration.

In the last few years, especially in the energy sector, a protocol standard has established itself which is now considered a “must-have” in substation automation and which is supported by virtually every component producer. We are talking about the international standards 60870-5-101 for serial communication, published in 1995 by the IEC, and 60870-5-104 for communication via TCP/IP, published in 2000.

Both protocols are identical on OSI layer 7 (Application), this means they have the same reference data structure and differ only physically in the implementation of OSI layers 1 to 4 (Physical – Transport). Thanks to that, it was easy to implement both the serial communication (-101) and the support for TCP/IP networks (-104) with the help of the modular driver architecture in the zenon IEC870 driver without having to bother about the physics of the actual handling of reference data and logic.

Basic Functions of IEC870

The protocol IEC 60870-5-10x defines that messages and values must be sent spontaneously from Slave (Controller) to Maser (PC) after a change, so there is no Polling procedure. After establishing the connection, the master sends a “general interrogation command" to the slave in order to get the current state of all data points. From this time on, the Slave watches for changes of the data points and sends only if required. The Master only sends commands and value changes to the Slave and remains passive otherwise.

Another specific feature of the protocol is the fact that a registration/deregistration of data points is not possible; this means, after a general query, the Slave sends a complete process image to the Master and the monitoring of changes also affects all data points.

Addressing scheme

The protocol differs between several data point types. What is particularly interesting: there is a difference between read-only and write-only data points.  A message, for example, is always read-only and a command is always write-only. As with usual PLC controllers, there are no data points that can be read and written.

We can distinguish between 3 different levels in the addressing scheme.   

The hardware address (the “link address” when using serial communication and the IP address when using TCP/IP) is on the top level. On the next level, we find the sector address. It usually serves for accommodating several independent “devices” behind a physical interface. This sector address is called “common address” (COA) in the protocol. Every sector has its own data point list. The data points are identified by the “information object address” (IOA).

So, to access a specific data point, four pieces of information are necessary: Hardware address, data point type, COA and IOA. (Example: “(192.168.0.100) T01 1.123" refers to the single information 123 in sector 1 in device 192.168.0.100)

Engineering

In zenon, the engineering of the IEC870 driver starts with the configuration of all connections in the driver. For this, the specific protocol parameters for every connection must be configured. These include, for example, the participant address, the number of bytes in COA and IOA and the length of the transmission cause (COT).  After that, the underlying sectors for every connection are defined.

The driver needs this information so that it can establish a connection including a general request. In the second step, any controller can read all the readable data points with the online import functionality in the editor; the data points are automatically created as zenon variables. In the third step, all the writable data points are created as variables in the usual way.

Diagnostics

The IEC870 driver supports a comprehensive set of diagnostic and logging functionalities. You can choose the level of detail to determine whether the log should include only basic information or detailed information right down to the byte level.  Of course, the usual error logging included in all zenon drivers is always active.