7-8
Section
Bit Control Instructions
380
Exercise caution when using a KEEP reset line that is controlled by an external
normally closed device. Never use an input bit in an inverse condition on the re-
set (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 situ-
ation is shown below.
A
Input Unit
A
NEVER
S
R
KEEP(11)
B
Bits used in KEEP are not reset in interlocks. Refer to the
7-11
INTERLOCK –
and INTERLOCK CLEAR IL(02) and ILC(03)
for details.
7-8-4 DIFFERENTIATE UP and DOWN – DIFU(13) and DIFD(14)
B
: Bit
IR, SR, AR, HR, LR
Ladder Symbols
Operand Data Areas
DIFU(13) B
B
: Bit
IR, SR, AR, HR, LR
DIFD(14) B
Any output bit can generally be used in only one instruction that controls its sta-
tus.
DIFU(13) and DIFD(14) are used to turn the designated bit ON for one cycle
only.
Whenever executed, DIFU(13) compares its current execution with the previous
execution condition. If the previous execution condition was OFF and the cur-
rent one is ON, DIFU(13) will turn ON the designated bit. If the previous execu-
tion condition was ON and the current execution condition is either ON or OFF,
DIFU(13) will either turn the designated bit OFF or leave it OFF (i.e., if the desig-
nated bit is already OFF). The designated bit will thus never be ON for longer
than one cycle, assuming it is executed each cycle (see
Precautions
, below).
Whenever executed, DIFD(14) compares its current execution with the previous
execution condition. If the previous execution condition was ON and the current
one is OFF, DIFD(14) will turn ON the designated bit. If the previous execution
condition was OFF and the current execution condition is either ON or OFF,
DIFD(14) will either turn the designated bit OFF or leave it OFF. The designated
bit will thus never be ON for longer than one cycle, assuming it is executed each
cycle (see
Precautions
, below).
These instructions are used when differentiated instructions (i.e., those prefixed
with an @) are not available and single-cycle execution of a particular instruction
is desired. They can also be used with non-differentiated forms of instructions
that have differentiated forms when their use will simplify programming. Exam-
ples of these are shown below.
Flags
There are no flags affected by these instructions.
Precautions
Limitations
Description