HEIDENHAIN PWM 20 - Manual (Page 221)

222 HEIDENHAIN ATS Software User's Manual
7.4 Absolute interface
7.4.1 EnDat
The EnDat interface (Encoder Data) of the absolute encoders is a bidirectional interface and
therefore able to output absolute position values as well as to request and update information
stored in the encoder. Thanks to serial data transfer four signal lines are sufficient. The
transfer mode (position values or parameters) is selected with MODE commands sent to the
encoder by the subsequent electronics. The data are transferred in synchronism with the
CLOCK signal prescribed by the subsequent electronics.
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.). For this purpose the interface protocol was expanded and the time
conditions (clock frequency, calculating 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
battery-buffered encoders).
EnDat 2.2 and
EnDat 2.1 versions The extended interface version EnDat 2.2 is compatible with the version 2.1 as regards
communication, command set (i.e. the available MODE commands) and time conditions,
but it offers significant advantages. For example, it is possible to transfer additional information
together with the position value without having to send a separate request. For this purpose the
interface protocol was expanded and the time conditions (clock frequency, calculating time,
recovery time) were optimized.
EnDat 2.1 and EnDat 2.2 are both available with or without incremental signals. The standard
version of EnDat 2.2. units is without incremental signals, since these units feature a high
internal resolution. To increase the resolution of EnDat 2.1 units, the incremental signals are
evaluated in the subsequent electronics.
Note
For detailed information on EnDat, refer to the technical information "EnDat 2.2 -
Bidirectional Interface for Position Encoders" (ID 383942-xx) and to our website
www.heidenhain.de.