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Introduction to Sercos interface
Applications Types
Sercos III
Sercos I and II
Fiber Optics
Timing & Interface
Sercos IDNs
I/O Functions
Cycle Times
Cyclic Operation
System Safety
Packaging Profile
Sercos Standardization

Sercos IDNs

All motion control and drive communication is performed via a set of Sercos interface telegrams, which each have an identification, or "Ident" (IDN) number. All parametric data, such as scaling and loop gains, and real-time loop closure information is set up this way. This allows the Sercos interface to standardize the most common interface data.

The Sercos interface standard allocates a block of 32,767 IDN numbers for standard commands. Over 500 of these are presently used to define a comprehensive set of motion control and I/O commands. All Sercos interface products must incorporate a subset of these, but do not necessarily need to include all IDNs.

The format used for an IDN in the IEC standard document is:


Name (abbreviation)
Length in bytes

Minimum input value
Maximum input value



Real-Time Data IDNs

The standard defines a number of IDNs for real time data. For example, in each communication cycle, the master transmits a Master Data Telegram that contains a series of IDNs (idents) specifying real-time operating data and drive commands for the addressed drive. A slave responds with an Amplifier Telegram containing 1 to 16 IDNs reporting data such as speed, torque and position measurements to the master, effectively closing the control loop.

Manufacturer-defined IDNs

In order to avoid restricting drive/control development, the IEC standard defines 32,767 vendor-defined IDNs that can be used by individual vendors to incorporate special features in their products. The standard provides that these vendor-defined IDNs only enable additionally functionality not already handled by standard functions, thus ensuring interoperability.

Vendor-defined IDNs have proven valuable in incorporating new features into the Sercos interface. A number of vendors have utilized the vendor-defined IDNs to introduce and field-prove some new control/drive feature. Later, these features have been incorporated into the standard IDN set for use in a standardized manner by all manufacturers.