
8-24
Ladder Logic (LAD) for S7-300 and S7-400
C79000-G7076-C504-02
8.23 Reset Set Flipflop
The Reset Set Flipflop instruction executes Set (S) and Reset (R) operations
only when the RLO is 1. An RLO of 0 has no effect on these operations; the
address specified in the operation remains unchanged.
A Reset Set Flipflop is reset if the signal state is 1 at the R input and 0 on the
S input. Otherwise, if the signal state is 0 at the R input and 1 at the S input,
the Flipflop is set. If the RLO is 1 at both inputs, the Flipflop is set.
The Reset Set Flipflop instruction is affected by the Master Control Relay
(MCR). For more information on how the MCR functions, see Section 20.5.
Certain restrictions apply to the placement of the Reset Set Flipflop box (see
Section 6.1).
Table 8-22 Reset Set Flipflop Box and Parameters
LAD Box
Parameter Data Type Memory Area Description
RS
<address>
<address> BOOL I, Q, M, D, L
The address indicates the bit that is to be
set or reset.
RQ
R BOOL I, Q, M, D, L Enabled reset operation
S
S BOOL I, Q, M, D, L Enabled set operation
Q BOOL I, Q, M, D, L Signal state of <address>
Status Word Bits
BR CC 1 CC 0 OV OS OR STA RLO FC
Write – – – – – x x x 1
I 0.0
If the signal state is 1 at input I 0.0 and 0
at input I 0.1, memory bit M 0.0 is reset,
and output Q 4.0 is 0.
Otherwise, if the signal state is 0 at input
I 0.0 and 1 at input I 0.1, memory bit
M 0.0 is set and Q 4.0 is 1.
If both signal states are 0, nothing is
changed. If both signal states are 1, the
Set operation dominates because of the
order, M 0.0 is set, and Q 4.0 is 1.
Q 4.0
M 0.0
RS
S
QR
I 0.1
Figure 8-22 Reset Set Flipflop
Description
Bit Logic Instructions
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