78
3-7-9 KEEP - KEEP(12)
B: Bit
Output bits, work bits, DR, LR
Ladder Symbol Operand Data Areas
S
R
KEEP(12)
B
Any output bit can generally be used in only one instruction that controls its
status. Refer to 3-2-2 I/O Bits for details.
KEEP(12) is used to maintain the status of the designated bit based on two
execution conditions. These execution conditions are labeled S and R. S is
the set input; R, the reset input. KEEP(12) operates like a latching relay that
is set by S and reset by R.
When S turns ON, the designated bit will go ON and stay ON until reset, re-
gardless of whether S stays ON or goes OFF. When R turns ON, the desig-
nated bit will go OFF and stay OFF until reset, regardless of whether R stays
ON or goes OFF. The relationship between execution conditions and
KEEP(12) bit status is shown below.
S execution condition
R execution condition
Status of B
KEEP(12) operates like the self-maintaining bit described in 3-6-5 Self-main-
taining Bits (Seal). The following two diagrams would function identically,
though the one using KEEP(12) requires one less instruction to program and
would maintain status even in an interlocked program section.
0002 0003
0100
0100
Address Instruction Operands
Address Instruction Operands
000 LD 0002
001 OR 0100
002 AND NOT 0003
003 OUT 0100
000 LD 0002
001 LD 0003
002 KEEP(12) 0100
S
R
KEEP(12)
0100
0002
0003
There are no flags affected by this instruction.
Never use an input bit in a normally closed condition on the reset (R) for
KEEP(12) when the input device uses an AC power supply. The delay in
shutting down the PC’s DC power supply (relative to the AC power supply to
the input device) can cause the designated bit of KEEP(12) to be reset. This
situation is shown below.
Limitations
Description
Flags
Precautions
Instruction Set Section 3-7
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