51
DIFU(13) and DIFD(14) operation can be tricky when used in programming
between IL and ILC, between JMP and JME, or in subroutines. Refer to
5–7
Interlock and Interlock Clear – IL(02) and ILC(03)
and
5–8 Jump and Jump
End – JMP(04)/JME(05)
for details. A total of 48 DIFU(13)/DIFD(14) can be
used in a program. If more than 48 are used in a program only the first 48 will
be executed and all others will be ignored. DIFU(13)/DIFD(14) are useful
when used in conjunction with CMP(20) or MOV(21), see
Example
below.
There are no flags affected by these instructions.
In diagram A, below, CMP(20) will compare the contents of the two operand
words (HR 1 and DM 00) whenever it is executed with an ON execution con-
dition and set the arithmetic flags (GR, EQ, and LE) accordingly. If the execu-
tion condition remains ON, flag status may be changed each scan if the con-
tents of one or both operands change. Diagram B, however, shows how
DIFU(13) can be used to ensure that CMP(20) is executed only once each
time the desired execution condition goes ON.
0000
CMP(20)
HR 1
DM 00
Diagram A
1000
CMP(20)
HR 1
DM 00
Diagram B
DIFU(13) 1000
0000
5–6–3 Keep – KEEP(11)
B: Bit
IR, HR
Ladder Symbol Operand Data Areas
KEEP(11)
B
R
S
Any output bit can be used in only one instruction that controls its status. See
3–3–1 I/O Words
for details.
KEEP(11) is used to maintain the status of the designated bit based on two
execution conditions. These execution conditions are labeled S and R. S is
the set input; R, the reset input. KEEP(11) operates like a latching relay that
is set by S and reset by R.
When S turns ON, the designated bit will go ON and stay ON until reset, re-
gardless of whether S stays ON or goes OFF. When R turns ON, the desig-
nated bit will go OFF and stay OFF until reset, regardless of whether R stays
ON or goes OFF. The relationship between execution conditions and
KEEP(11) bit status is shown below.
Flags
Example
Limitations
Description
Bit Control Instructions Section 5–6
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