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EnDat 2.2 – Overview of encoder characteristics

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.

More information: EnDat 2.2 Technical Information updated

One of the decisive advantages of the EnDat interface is the wide variety of available encoders for diverse applications. HEIDENHAIN product program of linear and angle encoders cover applications in the fields of machine tools, the electronics industry and automation technology. The requirements in these applications and sectors of industry are reflected in the various characteristics of the different encoder models. The characteristics are a mapped over the EnDat 2.2 interface and are reflected in the memory contents and position information formats of the encoder. The following pages provide an overview of characteristics of HEIDENHAIN encoders. The data shown here serve as a supplement, but not a replacement, for the Specifications of the respective encoder.

Explanations:

ID
ID number of the encoder

Functional safety
Does the encoder support functional safety? For more information, see the Specifications.

Calculation time
Processing time of encoder (“calculation time”) Time tCAL is the smallest time duration after which the position value can be read by the encoder. For more information, see the Specifications or the EnDat Application Note.

Bit width of position 1
The data word width of the transferred position value depends on the encoder. The transmission protocol must be flexibly adapted to this value. Usually the value is read from the encoder memory and the master is parameterized with this value.

Encoder type
In some cases, parameters must be interpreted differently for the various encoder types (see EnDat Specifications or Application Note) or EnDat additional data must be processed (e.g. incremental or battery-buffered encoders). The parameters required for operating the encoder and the supported functions are stored in the memory of the encoder. Further information on incremental or battery-buffered encoders can be taken from the EnDat Application Note.

A distinction is made between the following encoder types:

Encoder type: see EnDat 2.1 parameters, word 14 (bits 12 to 15)

Code

Linear encoder

Absolute

40

Absolute

With cyclic coding

60

Incremental

With distance-coded reference marks

10

Incremental

Without distance-coded reference marks

0

Incremental

With distance-coded reference marks

With battery buffer

30

Incremental

Without distance-coded reference marks

With battery buffer

20

Rotary or angle encoder

Absolute

Singleturn

C0

Absolute

Multiturn

With gears

E0

Absolute

Multiturn

With battery buffer

D0

Incremental

Singleturn, with distance-coded reference marks

90

Incremental

Singleturn, without distance-coded reference marks

80

Incremental

Singleturn, with distance-coded reference marks

With battery buffer

B0

Incremental

Singleturn, without distance-coded reference marks

With battery buffer

A0

Touch probes

50

Error messages
An error message is set if there is a malfunction in the encoder that could be causing incorrect position values. Up to 16 error messages can be distinguished, of which seven are presently occupied. Individual error messages are supported depending on the encoder.

Warning messages
Warnings show that the tolerance specifications for certain internal encoder parameters were exceeded. Over extended periods, this can trigger error messages. Warnings therefore enable the user to correct problems before they can cause errors. Individual error messages are supported depending on the encoder.

Diagnostics
Encoders with EnDat 2.2 can cyclically output so-called valuation numbers (BWZ) in order to evaluate the functions of the encoder. The valuation numbers provide the current state of the encoder and indicate the encoder’s “function reserves.” Their scaling is identical for all HEIDENHAIN encoders. This makes integrated evaluation possible.

  • BWZ 1: Valuation of the incremental or scanning track
  • BWZ 2: Free for future applications
  • BWZ 3: Valuation of the absolute track / (reference pulse width)
  • BWZ 4: Valuation of the position value formation / (reference pulse position)
  • System-specific interface:
    o In addition to the online diagnostics, certain encoders provide special information over the diagnostics interface for mounting, for example the mounting dimensions. For more information, see the EnDat Application Note or the Specifications.

Additional data
An encoder with EnDat 2.2 interface can transmit the position value together with up to two additional data. For more information on the contents of the transferred values, see “Technical Information EnDat 2.2.”

This overview does not take additional data into account that are always available (diagnostics, memory parameters, MRS code acknowledgment) or are reserved for future applications (additional sensors, commutation, acceleration, asynchronous position value, timestamp).

Brief description of the additional data in the table:

Position value 2
For incremental encoders: Relative position information (counter starts from zero at switch-on). The absolute position value is available only after the reference marks have been scanned. For absolute encoders: Second absolute position value for safety-related applications.

Temperature
Transmission of temperature in encoders with integrated evaluation of internal or external temperature sensors.

Limit position signals
Limit position signals and homing information.

Operating status error sources
Detailed information about the cause of the present error message (is needed, for example, for encoders with a battery-buffered revolution counter).

OEM
In this freely definable memory area, the OEM can store his information, e.g. the “electronic ID label” of the motor in which the encoder is integrated, indicating the motor model, maximum current rating, etc. The size is given in EnDat words (16-bis words).

Additional functions
The EnDat interface makes it possible to set various functions regarding data transmission or the general operation of the encoder. The settings are normally saved and need only be made once. Functions that are reserved for future applications are not listed in the table.

Datum shift
This function is called “electronic datum setting” and enables the customer to fit the encoder datum to the datum of the application. The datum shift can be write-protected.

The recovery time is adjustable
The recovery time is reduced when very short cycle times are to be attained.

Multiturn functions
Makes it possible to connect encoders with a battery-buffered revolution counter.

RM bit can be reset
Only for incremental encoders or EIB. The existing referencing is deleted and the referencing process, i.e. scanning the reference mark(s), is restarted.