Siemens LOGO! Series - Latching Relay

LOGO! functions
4.4 Special functions list - SF
LOGO!
228 Manual, 04/2011, A5E03556174-01
View in parameter assignment mode (example):
$4 
% 
$ 
%
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.
56
4
6
5
3DU
Output Q Q is set with a signal at input S, and reset with a
signal at input R.
Timing diagram
4
5
6
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.