52
Programming Restrictions
Section 2-4
• When the instance’s EN input variable goes ON, the present execution
condition status will not be compared to the last cycle’s status. The
present execution condition will be compared to the last condition when
the EN input variable was ON, so the Differentiation Instruction will not
operate properly. (If the EN input variable remains ON, the Differentiation
Instruction will operate properly when the next rising edge or falling edge
occurs.)
Example:
If Differentiation Instructions are being used, always use the Always ON Flag
(P_On) for the EN input condition and include the instruction’s input condition
within the function block definition.
• Input a decimal numerical value after “#” when specifying the first operand
of the following instructions.
MILH(517), MILR(518), MILC(519), DIM(631), MSKS(690), MSKR(692),
CLI(691), FAL(006), FALS(007), TKON(820), TKOF(821)
Note “&” is not supported.
• CNR(545), CNRX(547) (RESET TIMER/COUNTER) instructions cannot
be used to reset multiple timers and counters within a function block at the
same time.
Always specify the same variable for the first operand (timer/counter num-
ber 1) and second operand (timer/counter number 2). Different variables
cannot be specified for the first and second operand.
Timer Instructions in
Function Block Definitions
An instance will not be executed while its EN input variable is OFF, so the fol-
lowing precautions are essential when using a Timer Instruction in a function
block definition.
The Timer Instruction will not be initialized even though the instance’s EN
input variable goes OFF. Consequently, the timer’s Completion Flag will not be
turned OFF if the EN input variable goes OFF after the timer started operat-
ing.
FB1
EN ENO
IN1 OUT1
0.0
LD EN
OR IN1
SET OUT1
These Differentiation Instructions do not
operate when input condition 0.00 goes
from OFF to ON the first time.
The instructions do not operate while
input condition 0.00 is OFF.
Body
FB1
EN ENO
a O UT1
IN 1
P_On
LD a
OR IN1
SET OUT1
0.00
The EN input condition is always ON, so
these Differentiation Instructions operate
normally.
Body
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