EnDat 2.1 – Transmission of Position Values

Encoder saves position valueSubsequent electronics transmit mode command EnDat 2.1 can transmit position values with interrupted clock pulse (as in EnDat 2.2) or continuous clock pulse. Interrupted clock The interrupted clock is intended particularly for time-clocked systems such as closed control loops. At the end of the data word the clock signal is set to HIGH level. After 10 to 30 µs (t Encoder transmit position value is needed only before the fi rst data transmission, the continuous-clock transfer mode reduces the length of the clock-pulse group by 10 periods per position value.
m ), the data line falls back to LOW. A new data transmission can then begin when started by the clock.
Mode commandPosition valueCyclic Redundancy Check Continuous clock For applications that require fast acquisition of the measured value, the EnDat interface can have the clock run continuously. Immediately after the last CRC bit has been sent, the data line is switched to high for one clock cycle, and then to low. The new position value is saved with the very next falling edge of the clock and is output in synchronism with the clock signal immediately after the start bit and alarm bit. Because the mode command Absolute encoders with EnDat interface can exactly synchronize serially transmitted absolute position values with incremental values. With the fi rst falling edge (latch signal) of the CLOCK signal from the subsequent electronics, the scanning signals of the individual tracks in the encoder and industrial counter are frozen, as are the A/D converters for subdividing the sinusoidal incremental signals in the subsequent electronics.The code value transmitted over the serial interface unambiguously identifi es one incremental signal period. The position value is absolute within one sinusoidal period of the incremental signal. The subdivided incremental signal can therefore be appended in the subsequent electronics to the serially transmitted code value. Interrupted clock Synchronization of the serially transmitted code value with the incremental signal
Save new position valueSave new position value n = 0 to 7; depending on system Position valueCRCCRC Continuous clock
Latch signal SubdivisionCounter PP Comparator 1 V PP Parallel interface 1 V After power on and initial transmission of position values, two redundant position values are available in the subsequent electronics. Since encoders with EnDat interface guarantee a precise synchronization—regardless of cable length—of the serially transmitted absolute value with the incremental signals, the two values can be compared in the subsequent electronics. This monitoring is possible even at high shaft speeds thanks to the EnDat interface’s short transmission times of less than 50 µs. This capability is a prerequisite for modern machine design and safety systems.

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