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Never use an input bit in an normally closed 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 device) can cause the designated bit of KEEP(11) to be reset. This
situation is shown below.
Input Unit
A
NEVER
S
R
KEEP(11)
HR 000
A
Bits used in KEEP are not reset in interlocks. Refer to the
5-7 INTERLOCK
and INTERLOCK CLEAR – 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.
HR 000
0500
0002
0003
0004
0005
Reset input
Indicates
emergency
situation
Activates
warning
display
Address Instruction Operands
0000 LD 0002
0001 OR 0003
0002 OR 0004
0003 LD 0005
0004 KEEP(11) HR 000
0005 LD HR 000
0006 OUT 0500
S
R
KEEP(11)
HR 000
KEEP(11) can also be combined with TIM to produce delays in turning bits
ON and OFF. Refer to
5-11-1 TIMER – TIM
for details.
5-7 INTERLOCK and INTERLOCK CLEAR – IL(02) and ILC(03)
Ladder Symbol
IL(02)
Ladder Symbol
ILC(03)
IL(02) is always used in conjunction with ILC(03) to create interlocks. Inter-
locks are used to enable branching in the same way as can be achieved with
TR bits, but treatment of instructions between IL(02) and ILC(03) differs from
that with TR bits when the execution condition for IL(02) is OFF. If the execu-
tion condition of IL(02) is ON, the program will be executed as written, with
an ON execution condition used to start each instruction line from the point
where IL(02) is located through ILC(03).
Precautions
Example
Description
INTERLOCK and INTERLOCK CLEAR – IL(02) and ILC(03) Section 5-7