Siemens SIMATIC S5-90U System Manual page 503

S5-90U/S5-95U
Starting the Counter
The counter is reset and started by setting the SYNC bit in the diagnostic byte during the reference
point approach operation. The active pulses are counted according to the rotation direction of the
position encoder. The count value is incremented during a positive count direction, and decremen-
ted during a negative count direction.
Enabling the Outputs - Reaching the Setpoints - Resetting the Outputs
The two outputs are enabled for switching by a positive pulse edge at the enable input.
An output and the associated diagnostic bit "setpoint reached" are set if all of the following
statements are true.
• The position decoder was synchronized (SYNC bit=1 and overflow bit=0).
• The enable signal (terminal 3 on the terminal block) is set to "1" signal.
• The actual value corresponds to the selected setpoint.
The setpoint can be reached in the up-count or down-count direction.
SYNC Bit is set to begin
Counter status
0 1 2
Counting pulses
SYNC bit
(in diagnostic
byte
)
Enable
input
Output Q0
(setpoint 1
reached)
Output Q1
(setpoint 2
reached)
Measured counting pulse
Figure 16-22. Enabling the Outputs - Reaching the Setpoints - Resetting the Outputs
After reaching setpoint 1, the output Q 0 is energized and the status bit S 1 is set. After reaching
setpoint 2, the output Q 1 is energized and status bit S 2 is set.
As long as the enable input is active, the outputs are switchable through the module. If the enable
command is cancelled, the outputs are switched off and the diagnostic bits are reset. The current
actual value is still being measured and incremented or decremented depending on the direction of
rotation.
EWA 4NEB 812 6115-02b
Up-count direction
3 4 5 6 7 7 8 9 10
Counter is still disabled
Function Modules
Down-count direction
SYNC bit is constantly set
-10 -9 7 -8 -7 -6 -5 -4 -3 -2 -1 0 1
16-35