select the type of transmission, the subsequent electronics transmit the mode command “Encoder transmit position value” (with/without additional information).The subsequent electronics continues to transmit clock pulses and observes the data line to detect the start bit. The clock edge. The measured values are saved and the position value calculated. After two clock pulses (2T), to start bit Control cycles for transfer of position values The transmission cycle begins with the fi rst falling starts data transmission from the encoder to the subsequent electronics. Time t Mode commands

Selecting the transmission type

defi ne the content of the transmitted information. Every mode command consists of three bits. To ensure reliable transmission, every bit is transmitted redundantly (inverted or redundant). The EnDat 2.2 interface can also transfer parameter values in the additional information together with the position value. This makes the current position values constantly available for the control loop, even during a parameter request. Mode commands Transmitted data are identifi ed as either position values, position values with additional information, or parameters. The type of information to be transmitted is selected by mode commands. Encoder transmit position valueSelection of memory area Encoder receive parameters Encoder transmit parameters Encoder receive reset
1) Encoder transmit test values Encoder receive test command•• • • • • •
EnDat 2.1EnDat 2.2 • • • • • • • Encoder transmit position value with additional informationEncoder transmit position value and receive selection of memory area
2) Encoder transmit position value and receive parameters
2) Encoder transmit position value and transmit parameters
2) Encoder transmit position value and receive error reset
2) Encoder transmit position value and receive test command
2) Encoder receive communication command
3) 1) 2) Same reaction as switching the power supply off and on
3) Selected additional information is also transmitted Reserved for industrial encoders that do not support the safety systemThe time absolute linear encoders need for calculating the position values t Specifi cations in the Linear Encoders for Numerically Controlled Machine tools
cal differs depending on whether EnDat 2.1 or EnDat 2.2 mode commands are transmitted (see brochure). 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 mode commands should not be used for purely serial position-value transfer for axis control.
cal is the smallest time duration time after which the position value can be read by the encoder. The subsequent error messages, error 1 and error 2 (only with EnDat 2.2 commands), are group signals for all monitored functions and serve as failure monitors.Beginning with the LSB, the encoder then transmits the absolute Cyclic Redundancy Check (CRC).In EnDat 2.2, this is followed by additional information 1 and 2, each also concluded with a CRC. With the end of the data word, the clock must be set to HIGH. After 10 to 30 µs or 1.25 to 3.75 µs (with EnDat 2.2 parameterizable recovery time t position value as a complete data word. Its length depends on the encoder being used. The number of required clock pulses for transmission of a position value is saved in the parameters of the encoder manufacturer. The data transmission of the position value is completed with the Without delay compensationWith delay compensationClock frequency f
c 100 kHz ... 2 MHz100 kHz ... 16 MHz Calculation time for Position value Parameters t
cal See Specifi cations t
ac Max. 12 ms Recovery time t
m EnDat 2.1: 10 to 30 µs EnDat 2.2: 10 to 30 µs or 1.25 to 3.75 µs (f
c 1 MHz) (parameterizable) t
R Max. 500 ns t
ST –2 to 10 µs
m ) the data line falls back to LOW. Then a new data transmission Data delay time t
D (0.2 + 0.01 x cable length in m) µs can begin by starting the clock. Pulse width t
HI 0.2 to 10 µs0.2 to 50 ms/30 µs (with LC)Pulse width fl uctuationHIGH to LOW max. 10% t
LO

44