User Manual

LOGO! functions
4.4 Special functions list - SF
LOGO!
Manual, 06/2014, A5E33039675
197
4.4.23
Latching relay
Short description
Input S sets output Q, input R resets output Q again.
Symbol in LOGO!
Wiring
Description
Input S
You set output Q with a signal at input S.
Input R You reset output Q with a signal at input R. If S and R
= 1, the output is reset.
Parameter Retentivity:
/ = no retentivity
R = the status is retentive.
Output Q Q is set with a signal at input S, and reset with a
signal at input R.
Timing diagram
Switching response
A latching relay represents a simple binary element. The output value depends on the status
at the inputs and on the previous output status. The following table shows the logic once
again:
S
n
R
n
Q
Comment
0
0
x
The status is retentive
0
1
0
Reset
1
0
1
Set
1
1
0
Reset (takes priority over Set)
When retentivity is enabled, the current status of the output signal is retained after a power
failure.