Functional Safety

HEIDENHAIN offers encoders that can be used in safety-related applications. These encoders operate as single-encoder systems with purely serial data transmission via EnDat 2.2. Reliable transmission of the position is based on two independently generated absolute position values and on error bits, which are then provided to the safe control.

Information on implementing an EnDat Master for safety-related applications:

General information:

HEIDENHAIN offers rotary, angle and linear encoders with EnDat 2.2 interface that are suitable for safety-related applications. In order to be able to use these encoders in safety-related applications, a control is required for the appropriate evaluation and processing of the encoder data. The requirements for implementation are specified in a separately available documentation from HEIDENHAIN. This documentation describes, for example, the monitoring functions, specifications on the evaluation and processing of position values and error bits, and provides information about the electrical connection. An EnDat master for safety-related applications can be developed using the HEIDENHAIN documentation as a basis. However, developing and testing a safe EnDat master requires a lot of effort. MAZeT therefore offers a tested EnDat master for use in FPGAs/ASICs. The EnDat master was developed and tested together with HEIDENHAIN. This makes the implementation of a safe EnDat 2.2 interface a lot easier for the customer. The following is an overview of the various documents from HEIDENHAIN and MAZeT. Also, various possibilities for implementing the MAZeT EnDat master are described.

Documentation:

HEIDENHAIN
The documentation contains general information on the implementation of the EnDat 2.2 system, as well as specific information that applies only in conjunction with the MAZeT EnDat master.

General requirements

  • Technical Information brochure “Safety-Oriented Position Measuring Systems”
  • Specification of the safety requirements for the EnDat Master and measures for the safe control
  • Requirements for the position value comparison (EnDat-Master / control)
  • Specification of the EnDat 2.2 interface
  • Electrical Connection Directive

Specific specifications—only apply when using the MAZeT EnDat master

  • Test plan for type examination of EnDat master with safety functions
  • Specification of safety-related requirements to be fulfilled in addition in order to attain SIL 3, PL e, Cat 4 with suitable encoders

MAZeT
The EnDat Master Safety is available as a version with bidirectional 16-bit microcontroller interface or with APB interface. The V plan and the V protocol for the RTL level are also included.

  • EnDat Master Safety data sheet
  • Verification plan
  • Verification protocol

MAZeT EnDat master:

The EnDat master from MAZeT is a soft macro for FPGAs/ASICs, which can be transferred in various formats (e.g. VHDL). The EnDat master encapsulates the EnDat communication with the encoder and contains the necessary safety functions. The system is designed so that the tested core of the EnDat master is applied unchanged in the customer’s application. Only in this way can simplified validation steps be made possible. Custom-designed modules, such as different interfaces, can nevertheless be “docked” to the EnDat master. These expansions can be taken care of both by the customer and by MAZeT. A one-time fee is charged by MAZeT for the soft macro of the EnDat master with APB or 16-bit microcontroller interface. Additional custom-designed modifications must be defined separately by contract between the control manufacturer and MAZeT. The implementation and verification of the code in a customer’s application are subject to the requirements of the relevant safety standards (e.g. IEC 61508). The example in the figure below shows various verification possibilities for the individual implementation steps. Validation takes place as a part of the type examination of the customer’s application.