Omron CP - PROGRAMMING MANUAL 05-2007 Programming Manual page 151

Sequence Output Instructions
Flags
Precautions
118
KEEP(011) can be used to create flip-flops as shown below.
If a holding bit is used for B, the bit status will be retained even during a power
interruption. KEEP(011) can thus be used to program bits that will maintain
status after restarting the PLC following a power interruption. An example of
this that can be used to produce a warning display following a system shut-
down for an emergency situation is shown below.
0.02
0.03
Indicates
emergency
situation
0.04
0.05
Reset input
H0.00
The status of I/O Area bits can be retained in the event of a power interruption
by turning ON the IOM Hold Bit and setting IOM Hold Bit Hold in the PLC
Setup. In this case, I/O Area bits used in KEEP(011) will maintain status after
restarting the PLC following a power interruption, just like holding bits. Be sure
to restart the PLC after changing the PLC Setup; otherwise the new settings
will not be used.
No flags are affected by KEEP(011).
Never use an input bit in a normally closed condition on the reset (R) for
KEEP(011) when the input device uses an AC power supply. The delay in
shutting down the PLC's DC power supply (relative to the AC power supply to
the input device) can cause the operand bit of KEEP(011) to be reset. This sit-
uation is shown below.
Input Unit
A
NEVER
A
The operands for KEEP(011) are input in a different order in ladder diagrams
and mnemonic code.
Ladder diagram order: Set input
Mnemonic code order: Set input
H0.00
100.00
Activates
warning
display
S
KEEP
120000
R
KEEP(011) Reset input
Reset input KEEP(011)
Section 3-3