52
S execution condition
R execution condition
Status of B
Notice that KEEP(11) operates like a self-maintaining bit. The following two
diagrams would function identically, though the one using KEEP(11) requires
one less instruction to program and would maintain status even in an inter-
locked program section.
0002 0003
0500
0002
0003
0500
KEEP
0500
S
R
There are no flags affected by this instruction.
Never use an input bit in an inverse condition on the reset (R) for KEEP(11)
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 de-
vice) can cause the designated bit of KEEP(11) to be reset. This situation is
shown below.
KEEP
HR
000
A
S
R
Input Unit
A
NEVER
Bits used in KEEP are not reset in interlocks. Refer to the
5–7 Interlock –
IL(02) and ILC(03
) for details.
If a HR bit is used, bit status will be retained even during a power interrup-
tion. KEEP(11) can thus be used to program bits that will maintain status af-
ter restarting the PC following a power interruption. An example of this that
can be used to produce a warning display following a system shutdown for
an emergency situation is shown below. Bits 0002, 0003, and 0004 would be
turned ON to indicate some type of system error. Bit 0005 would be turned
ON to reset the warning display. HR 000, which is turned ON for any of the
three bits which indicates emergency situation, is used to turn ON the warn-
ing indicator through 0500.
Flags
Precautions
Example
Bit Control Instructions Section 5–6
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