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Motion Control Resources

EnDat 2.2 – Bidirectional Interface for Position Encoders

Heidenhain Corp.

Digital drive systems and feedback loops with position encoders for measured value acquisition require fast data transfer with high transmission reliability from the encoders. Further data such as drive-specific parameters, compensation tables, etc. must also be made available. For high system reliability, the encoders must be integrated in routines for error detection and have diagnostic capabilities.

The EnDat interface from HEIDENHAIN is a digital, bidirectional interface for encoders. It is capable both of transmitting position values from incremental and absolute encoders as well as transmitting or updating information stored in the encoder, or saving new information. Thanks to the serial transmission method, only four signal lines are required. The data are transmitted in synchronism with the clock signal from the subsequent electronics. The type of transmission (position values, parameters, diagnostics, etc.) is selected through mode commands that the subsequent electronics send to the encoder. The EnDat 2.2 interface, a purely serial interface, is also suited for safety-related applications up to SIL 3.

EnDat 2.2

The EnDat interface provides everything needed to reduce system cost and at the same time improve your technical standard. The most significant benefits are:

Cost optimization

  • A single interface for all absolute and incremental encoders
  • Simple subsequent electronics with EnDat receiver chip and standard components
  • Simpler, more economical voltage supply, since remote sensing is not required
  • Simple connection technology: Standard connecting elements (M12 – 8-pin), single shielded standard cables and low wiring costs
  • Only one cable with HMC 6: the Hybrid Motor Cable contains the lines for the encoder, the motor and the brake
  • Small motor or system dimensions through compact connecting elements
  • No expensive additional sensory analysis and wiring: EnDat 2.2 transmits additional data (limit switch, temperature, etc.)
  • Faster configuration during installation: Datum shifting through offsetting by a value in the encoder

Improved quality

  • Higher system accuracy through specific optimization in the encoder
  • High contour accuracy, particularly for CNC machine tools: position value formation in the encoder permits shorter sampling intervals without influencing the computing time of the CNC

Higher availability

  • Automatic configuration of the system axis: all necessary information can be saved in the encoder (electronic ID label).
  • High system reliability through purely digital data transmission
  • Diagnostics of the encoders through monitoring messages and warnings that can be evaluated in the subsequent electronics
  • High transmission reliability through cyclic redundancy checking

Safety system

  • EnDat 2.2 was conceived for safetyrelated machine designs up to SIL 3
  • Two independent position values for error detection
  • Two independent error messages
  • Checksums and acknowledgments
  • Forced dynamic sampling of error messages and CRC formation by subsequent electronics

Support for state-of-the-art machine designs

  • Suitable for direct drive technology thanks to high resolution, short cycle times and commutation information
  • Cyclic sampling every 25 μs with full “read and write” mode
  • Position values available in the subsequent electronics after only approx. 10 μs

EnDat Interface

The EnDat interface is a digital, bidirectional interface for encoders. It is capable both of transmitting position values as well as transmitting or updating information stored in the encoder, or saving new information. Thanks to the serial transmission method, only four signal lines are required. The data is transmitted in synchronism with the clock signal from the subsequent electronics. The type of transmission (position values, parameters, diagnostics, etc.) is selected through mode commands that the subsequent electronics send to the encoder. Some functions are available only with EnDat 2.2 mode commands.

History and compatibility
The EnDat 2.1 interface available since the mid-90s has since been upgraded to the EnDat 2.2 version (recommended for new applications). EnDat 2.2 is compatible in its communication, command set and time conditions with version 2.1, but also offers significant advantages. It makes it possible, for example, to transfer additional data (e.g. sensor values, diagnostics, etc.) with the position value without sending a separate request for it. This permits support of additional encoder types (e.g. with battery buffer, incremental encoders, etc.). The interface protocol was expanded and the time conditions (clock frequency, processing time, recovery time) were optimized.

Supported encoder types
The following encoder types are currently supported by the EnDat 2.2 interface (this information can be read out from the encoder’s memory area):

  • Incremental linear encoder
  • Absolute linear encoder
  • Rotational incremental singleturn encoder
  • Rotational absolute singleturn encoder
  • Multiturn rotary encoder
  • Multiturn rotary encoder with battery buffer

In some cases, parameters must be interpreted differently for the various encoder models (see EnDat Specifications) or EnDat additional data must be processed (e.g. incremental or batterybuffered encoders).

Interface EnDat serial bidirectional
Data transfer Position values, parameters and additional data
Data input Differential line receiver according to EIA standard RS 485 for the signals CLOCK, CLOCK, DATA and DATA
Data output Differential line driver according to EIA standard RS 485 for DATA and DATA signals
Position values Ascending during traverse in direction of arrow (see dimensions of the encoders)
Incremental signals Depends on encoder
» 1 VPP, TTL, HTL (see the respective incremental signals)

Order designations
The order designations define the central specifications and give information about:

  • Typical voltage supply range
  • Command set
  • Availability of incremental signals
  • Maximum clock frequency

The second character of the order designation identifies the interface generation. For encoders of the current generation the order designation can be read out from the encoder memory.

Incremental signals
Some encoders also provide incremental signals. These are usually used to increase the resolution of the position value, or to serve a second subsequent electronics unit. Current generations of encoders have a high internal resolution, and therefore no longer need to provide incremental signals. The order designation indicates whether an encoder outputs incremental signals:

  • EnDat01 With 1 VPP incremental signals
  • EnDatH With HTL incremental signals
  • EnDatT With TTL incremental signals
  • EnDat21 Without incremental signals
  • EnDat02 With 1 VPP incremental signals
  • EnDat22 Without incremental signals

Note on EnDat01/02:
The signal period is stored in the encoder memory.

Voltage supply
The typical voltage supply of the encoders depends on the interface:

EnDat01
EnDat21
5 V ± 0.25 V
EnDat02
EnDat22
3.6 V to 5.25 V or 14 V
EnDatH 10 V to 30 V
EnDatT 4.75 V to 30 V

Exceptions are documented in the Specifications.

Command set
The command set describes the available mode commands, which define the exchange of information between the encoder and the subsequent electronics. The EnDat 2.2 command set includes all EnDat 2.1 mode commands. In addition, EnDat 2.2 permits further mode commands for the selection of additional data, and makes memory accesses possible even in a closed control loop. When a mode command from the EnDat 2.2 command set is transmitted to an encoder that only supports the EnDat 2.1 command set, an error message is generated. The supported command set is stored in the encoder’s memory area:

  • EnDat01/21/H/T   Command set 2.1 or 2.2
  • EnDat02/22          Command set 2.2

To view the rest of this article, please follow this link to the full technical article from Heidenhain Corp.

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