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DR. JOHANNES HEIDENHAIN GmbH is a leading manufacturer of precision measurement and control equipment. Our superior technology is utilized in high-precision motors, motion control and machining systems worldwide. With over 100 years in the precision measurement industry, HEIDENHAIN is setting the future standards of position feedback accuracy today. Our primary industries are metalworking, machine tool, semiconductor and electronics, motor/drive, general automation, and medical, but can be of service anywhere highly dependable precision measurement and motion control is needed.

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EnDat 2.2 – Bidirectional Interface for Position Encoders

POSTED 05/13/2015

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.

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

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.

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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: