Siemens SIMATIC ET 200S Operating Instructions Manual page 107

Pulse and Direction
The level at direction input B is used as the direction setting.
An unwired input corresponds to the "Up" count direction if you have selected
"Pulse/direction" for the "Signal evaluation" parameter.
Figure 2-45
Rotary Transducer
The 1Count24V/100kHz can count the edges of the signals. Normally, only the edge at A is
evaluated (single evaluation). To obtain a higher resolution, at parameter assignment you
can select whether the signals are to be subjected to single, double, or quadruple evaluation.
Multiple evaluation is only possible with asymmetric 24 V incremental encoders with A and B
signals that are 90 degrees out of phase.
Single Evaluation
Single evaluation means that only one edge of A is evaluated; up count pulses are recorded
at a rising edge at A and low level at B, and down count pulses are recorded at a falling edge
at A and low level at B.
The diagram below illustrates the single evaluation of the signals.
Figure 2-46
Technological Functions
Operating Instructions, 02/2007, A5E00124867-05
Signals of a 24-V Pulse Generator with Direction Indicator
Single Evaluation
2.9 Evaluation of count and direction signal
1Count24V/100kHz
107