HEIDENHAIN

DR. JOHANNES HEIDENHAIN GmbH

Postfach 1260

83292 Traunreut

(08669) 31-0

info@heidenhain.de

http://www.heidenhain.de

Vis alle: / Skjul alle:

What is the simplest method for setting up EnDat communication with an encoder?

Example for minimum implementation:

1) Set the EnDat clock frequency to 300 kHz

2) Reset the encoder
Send “Encoder receive reset” mode command to the encoder

3) Clear the errors (also see “Sequences and Data Structures”)
The following mode commands are necessary for this (all values given in hexadecimals)
• Selection of the memory area (MRS code 0xB9)
• Encoder receive parameter (address 0x00 and parameter 0x0000)
• Encoder receive reset

4) Clear the warnings (also see “Sequences and Data Structures”)
The following mode commands are necessary for this (all values given in hexadecimals)
• Selection of the memory area (MRS code 0xB9)
• Encoder receive parameter (address 0x01 and parameter 0x0000)
• Encoder receive reset

5) Check whether the expected encoder is actually connected. The test is based on the ID number of the encoder, in this example for the LIC 4000.
The following mode commands are necessary for this (all values given in hexadecimals)
• Selection of the memory area (MRS code 0xA3)
• Encoder send parameter (address 0x08); buffer the result
• Encoder send parameter (address 0x09); buffer the result
• Encoder send parameter (address 0x0A); buffer the result
It must now be checked whether the ID number matches the expectation. In this example (LIC with ID 651 871-01) the memory content should be as follows:
• Address 0x08  Memory content 0x3031
• Address 0x09  Memory content 0xF25F
• Address 0x0A  Memory content 0x0009
These contents correspond to the ID number above (see the EnDat Specification: EnDat 2.2 parameters of the encoder manufacturer, Words 24 to 26)

6) The LIC 4000 permits EnDat clock frequencies up to 16 MHz; as a result:
• Active propagation-delay compensation
• Set the desired EnDat transmission frequency

7) Cyclical reading out of the position can be started

Which status messages does an EnDat transmission have, or which status messages should be checked?

The EnDat interface distinguishes between the following status messages:

Error message:

An error message is set if there is a malfunction in the encoder that could be causing incorrect position values. Depending on the mode command used for position value transmission, F1, or F1 and F2 are transmitted (see also EnDat specification).

 

Cyclic Redundancy Check (CRC):

In order to detect errors resulting from interference during data transmission, a 5-bit CRC code is assigned to every data word. The CRC code is generated by hardware in the encoder. The evaluation in the subsequent electronics can also be realized with the hardware. All one-bit errors in data transmission can be detected by means of the CRC. The detection of high-order data transmission errors depends on the data word length and the data contents. The error bit is included in the formation of the CRC code.

EnDat error types I, II and III:

 

Error type I:

This error type indicates that the transmission from the subsequent electronics to the encoder is disturbed, e.g. if the mode word was not received correctly (see EnDat specification). If a transmission does not conclude, then the error message is contained in the subsequent transmission.

 

Error type II:

This error type indicates an error during addressing, e.g. non-supported address was selected (see EnDat specification).

 

Error type III:

This error type indicates an error during selection of the additional information, for example if a non-supported additional information is selected (see EnDat specification).

 

When evaluating an EnDat transmission, you should always check all statuses and derive appropriate measures from them. The CRC, in particular, is a central element of data backup. The CRC of every data transfer should therefore be checked.

 

Error message(s) set, CRC OK and no EnDat error type:
- There is a malfunction in the encoder

CRC is incorrect:
- Noise in transmission path
- Also occurs in EnDat error type I
- Error messages can occur

EnDat error type I occurs:
- For causes, see EnDat specification (e.g. mode commands are not transmitted correctly)
- EnDat error messages can occur
- CRC is incorrect

EnDat error types II and III occur:
- For causes, see EnDat specification
- The selected addresses or MRS codes should be checked

 

Please note:

Measures to be taken for safety-relevant applications according to IEC 61508 and EN 13849 are described in the EnDat package of measures (D533095).

Which HEIDENHAIN encoders can be connected to the MASTERDRIVES by SBM2 card?

Certain hardware and software combinations of the MASTERDRIVES inverters erroneously send a clock or entire clock-pulse group in the boot phase of the connected position measuring system. If the encoder is driven by a clock during the boot phase, this can lead to an interruption of the boot procedure and output of incorrect position values.

SIEMENS initiated a redesign of the MASTERDRIVES electronics (SBM 2) and developed appropriate software. These modifications will be available starting in Dezember 2008 approximately. To ensure functional combinations of encoders and MASTERDRIVES for the transition period, HEIDENHAIN will modify, upon request, PCBs of the standard rotary encoders of the 35-mm and 56-mm series with optical scanning and deliver them in limited quantity. They can be distinguished by the index after the serial number according to the enclosure.

The following procedure is recommended to find out whether a combination of MASTERDRIVES and HEIDENHAIN encoder is functional:

• Compare the ID number and the index of the serial number (letter at the end of the serial number) of the HEIDENHAIN encoder on the ID label with the encoders included in the attached list. See also the two attached examples of HEIDENHAIN ID labels.
• If the index of the serial number is lower than the one indicated, please refer to your contact person within the HEIDENHAIN Sales department. Indicate the serial and ID numbers of the encoder and mention these FAQ.
• If the index of the serial number is equal or higher, there should be no problems with the MASTERDRIVES inverter.   

Index of Encoders

When Must the Change in Data Direction Occur?

 

1st clock period:	The driver in the encoder is deactivated
2nd clock period:	The driver in the subsequent electronics is activated
3rd to 8th clock period:	Transmission of the mode word
9th clock period:	The driver in the subsequent electronics is deactivated
10th clock period:	The driver in the encoder is activated

 

 

Is it Necessary to Transmit the Correct Number of Clock Pulses to the Encoder?

Yes!

• Before the first position-value request, word 13 of the EnDat 2.1 parameters must be read out, so that the subsequent electronics can correctly determine the number of clock pulses to be sent. EnDat 2.1 commands must be used to read out the information. 
• If not enough clock pulses are transmitted, then some information will not be available to the user, and the encoder hangs in the middle of the communication cycle. So under certain circumstances, the next communication will fail. 
• If too many clock pulses are transmitted, then the encoder interprets this as a continuous clock. The encoder is then within a communication cycle again, and under circumstances the next communication will fail. 
• The communication with the encoder may seem to be functioning, but if the timing changes slightly, for example, it will fail suddenly. Sporadic communication errors can also occur.

How Do I Correctly Program the OEM Memory Range?

• In principle the memory is freely programmable. HEIDENHAIN does not have requirements for the contents of the programming. 
• The memory is divided into four areas. These areas can be used either by the OEM (parameters of the OEM areas 1..4) or by the encoder manufacturer for compensation values (compensation values area 1..4). 
• The content of the compensation-value areas is not of interest to the user. 
• The EnDat 2.1 parameters (words 9-12, interrogation of words 9 and 10 suffices) contain information on whether the OEM range is supported, and which addresses within an available range can be addressed. 
• Different families of encoders support different OEM memory ranges and different address ranges. Therefore, the assignment of the OEM ranges must be read out for each and every encoder. 
• For this reason, the subsequent electronics should form addresses relative to the determined values, and not use absolute addresses. The programming must be adapted to the individual encoder. 

  

Error Messages Are Set After Power-On. Why?

• After the encoder has been powered, error messages can be set. Also refer to the EnDat specification. 
• For this reason, active errors and warnings should be cleared after powering the encoder. 
• If there really is an error in the encoder, the error bit will be set again during the next position request.  

Other information regarding errors and warnings: 

•  It is possible to reset the error word. It is not possible to reset individual error bits (see the specification). 
• A given encoder does not necessarily support all alarms. The alarms supported can be read from the encoder. Alarms not supported should be masked out. 
• This way the control can determine whether the errors demanded by the application are even supported. 
• HEIDENHAIN can assign even more error messages in the future!

 
 

Can Write-Protection be Rescinded Once It Is Set?

• Once write-protection has been activated, it cannot be rescinded.
• The encoder must be sent to the Service department at HEIDENHAIN,where the write-protection can be removed.  

How to Order designations are available for instrumentation EnDat and why?

Interface	Version	Clock frequency	Ordering information
EnDat 2.1	With incremental signals	< 2MHz	EnDat 01
EnDat 2.1	Without incremental signals	< 2MHz	EnDat 21
EnDat 2.2	With incremental signals	< 2MHz	EnDat 02
EnDat 2.2	Without incremental signals	< 8MHz (bzw. 16 MHz)	EnDat 22

Bold: Standard version

• Distinguishing features between EnDat 2.1 and 2.2:
  Supply voltage and clock frequency; not command set! 
• The ordering designation is indicated on the ID label.
• In the future, EnDat 2.1 encoders (EnDat 01 or 21) can also have the 2.2 command set! 
• The clock frequency is based on the properties of the encoder (especially for pluggable cable assemblies and EnDat 02) 
• Service encoders: Pay attention to the parameters!  

What Must Be Paid Attention to If the Clock for the Encoder Must Be Interrupted During Communication, e.g. Due to an Interrupt?

• If the clock must be interrupted during communication, the clock level must be kept at low. The encoder would interpret a high level for > 10 µs (or > 1.25 µs with reduced recovery time) as the end of the recovery time I, and therefore as the end of the communication cycle.  
• With the exception of the LC (max. 30 µs), the clock level can be held at low for several ms.  

What Must Be Considered when Selecting the Maximum Clock Frequency?

EnDat 2.1	The maximum permitted clock frequency depends on the maximum cable length. This results from the answer from the control also needing to be read in within one clock. The encoder places the data on the line with the rising clock edge. It is recommended that the control assume the data with the rising clock edge of the subsequent clock.
EnDat 2.2	In order to increase the clock frequency, propagation delay compensation (see EnDat specification) is performed. After power-on, but before propagation delay compensation is performed, the clock frequency must be limited to 300 kHz.

What must be taken into account for the shortened recovery time

The EnDat interface provides the possibility to reduce the recovery time for EnDat 2.2 mode commands (see EnDat specification). The reduction of the recovery time makes the realization of very short cycle times possible. The reduced recovery time led to misunderstandings regarding the specification data:

•  The reduction of the recovery time is only allowed for EnDat 2.2 mode commands. EnDat 2.1 commands must always be sent with the standard recovery time of 10 .. 30 µs.
• The reduced recovery time must only be set once, because the setting is stored in the EEPROM.
• If the reduction of the recovery time is set by the customer (see EnDat specification), then only mode commands (2.1 or 2.2) with high frequency may be sent after the first EnDat 2.2 mode command with high frequency (> 1 MHz) has been sent. Switching back to the slow frequency (< 1 MHz) and EnDat 2.1 mode commands can cause problems with certain encoders because this operating mode is not available.
• If it is necessary to switch from high frequency (> 1 MHz) to low frequency, the following sequence should be followed:
  1) Deactivation of all selected additional information
  2) Transmission of an EnDat 2.1 command with high transmission frequency
  3) Switchover to low transmission frequency
   

Recommendations:

• The shortened recovery time should only be used if this is necessary for reducing the cycle times.
• If the reduced recovery time is used, only EnDat 2.2 mode commands should be used in closed-loop control operation.
• Avoid switching from high to low transmission frequencies. 

Do I have to poll the start bit during a position request?

In the diagram in the EnDat specification it appears as if, after sending the mode word, I have to keep the clock at LOW, wait at least the time tCAL, and then the start bit appears immediately with the first clock pulse. I tried that with an encoder, and it worked. Is this correct, or do I continually have to send clock pulses and poll the start bit?
A waiting period of 1 ms must be maintained when switching.


Answer:
Unfortunately this is an incorrect interpretation of the diagram. It cannot be guaranteed that the behavior you described applies to all different encoder models. The dashed lines in the diagram indicate that the clock must continue to be sent to the encoder. The start bit must be polled; i.e. clock pulses must be sent until the start bit is sent. That is what the dashed lines in the diagram indicate. The EnDat 2.1 specifications and the EnDat 2.2 specifications refer to Appendix A4 and Appendix A5, respectively, several times. The timing for the EnDat 2.1 position command is described in Appendix A4/A5. Continued clocking while polling the start bit is described there. The time tCAL indicates the earliest possible time at which the position value can be retrieved from the encoder. The start bit must be polled independently of tCAL.  

 

Parameters of the encoder manufacturer

<media 396 - download-plus>EnDat Parameters</media>

Special characteristics of the LC 183 / LC 483 with EnDat02 interface:

Due to the new scope of features of the EnDat02 interface, several encoder parameters differ from those of the predecessor encoders. For example, the measuring step was reduced from 100 nm to 5 nm, the OEM area was expanded, ….<br>Because it is now possible to control the axis “purely serially” or “with sinusoidal signals,” the LC xx3 encoders have some special characteristics that must be noted for correct operation of the encoders.   
 
EnDat 2.1 and 2.2 position requests
he time absolute linear encoders need for calculating the position values (tcal) differs depending on whether EnDat 2.1 or EnDat 2.2 mode commands are transmitted (see the encoder specifications). If the incremental signals are evaluated for axis control, then the EnDat 2.1 mode commands should be used. Only in this manner can an active error message be transmitted synchronously with the currently requested position value.
EnDat 2.1 or EnDat 2.2 mode commands can be used for pure serial position-value transfer for axis control. Position requests with EnDat 2.1 take about 1 ms until the position values are available.
For position requests with EnDat 2.2, the position values can be determined in about 5 µs. However, any active error message can then only be transmitted after a delay of approx. 1 ms, due to internal processing times.
A one-time position request with EnDat 2.2 may not be performed.  

Continuous clock (only possible with EnDat 2.1 position requests)   
Is not supported.  

Clock interruptions 
A clock interruption during the LOW phase may not last longer than 30 ?s.. 

Interruption of an EnDat request 
The subsequent position request is not valid, and the encoder reacts with error type I or II.  

Invalid memory access (incorrect MRS code)
Interruption of an EnDat request
Is at first acknowledged by the encoder with error type II.
The subsequent position request transmits the last position value transmitted. No error message is output:
EnDat 2.1 position request: One-time
EnDat 2.2 position request: Up to 1 ms

Switching between EnDat 2.1 and EnDat 2.2 commands (either direction): 
A waiting period of 1 ms must be maintained when switching. 

 

What Is the Recommended Procedure After Power-On?

 

What needs to be considered during booting of the encoder?

 

 

Caption

(1)	The rise time of the supply voltage until Up,min is reached should be > 10 V/sec.
(2)	The time until the 1-VPP incremental signals assume valid values is max. 1.3 sec.
(3)	The encoder can be recognized as an EnDat or SSI encoder by the logic level on the data line, after power has been switched on.
(4)	Clock pulse edges during t1 or t2 can interrupt booting; this can only be corrected by switching the encoder off and then on again.
(5)	A first EnDat request (falling edge) is permissible once t3 has ended after at least 1 ms (there is no maximum time limit). After the first clock pulse, the direction of data on the data line is reversed (this is why the data line is then at “high impedance”).
(6)	The encoder requires a defined reset: Falling edge + end of recovery time; During the Low phase this is 0.125 < tlow < 30 µs
(7)	t1: Boot or reset time of the EnDat encoder t2: Initialization phase of the EnDat encoder t3: Must be maintained for downward compatibility to EnDat 2.1

 

 

Which EnDat Masters are Available on the Market?

EnDat 2.1

An ASIC is available from MAZeT  (www.mazet.de)

EnDat 2.2

• EnDat Master Standard
• EnDat Master Reduced (only EnDat Protocol Machine)
• EnDat Master Light (only EnDat Protocol Machine)

 

 

Implementation

Which Data Width Should Be Made Available to EnDat Encoders? Are 32 Bits Enough?

EnDat 2.1	Maximum 40-bit data width for the position value.
EnDat 2.2	Maximum 48-bit data width for the position value.
In general	It is recommended that the maximum possible data widths be available, so that future generations of encoders can also be connected. The trend is towards ever higher resolutions.
32-bit data width	Definitively not enough. For example, the EQN 1337 has 12-bit multiturn and 25-bit singleturn resolution, for a total of 37 bits of position information.

Which encoder profiles or encoder types does EnDat support?

The supported encoder types can be taken from the “parameters of the encoder manufacturer,” word 14:

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

In some cases, parameters must be interpreted differently for the various encoder types (see EnDat Specifications) or EnDat additional information must be processed (e.g. incremental or battery-buffered encoders). Further information on incremental or battery-buffered encoders can be taken from the EnDat Application Note.

The various parameters must be taken into account for EnDat implementation or for testing the implementation.

What must be considered with incremental encoders with EnDat interface?

The EnDat additional information must be processed for the connection of incremental encoders; For details, see the EnDat Application Note.
The EnDat Master light cannot be used.