Keep; Self-Maintaining Bits (Seal) - Omron SYSMAC CVM1 Series Operation Manual

Controlling Bit Status

4-7-3 KEEP

0000 0000
02 03
0000
04
0000
05

4-7-4 Self-maintaining Bits (Seal)

0002 0000
00 03
0000
00
86
The KEEP instruction is used to maintain the status of the operand bit based on
two execution conditions. To do this, the KEEP instruction is connected to two
instruction lines. When the execution condition at the end of the first instruction
line is ON, the operand bit of the KEEP instruction is turned ON. When the
execution condition at the end of the second instruction line is ON, the operand
bit of the KEEP instruction is turned OFF. The operand bit for the KEEP instruc-
tion will maintain its ON or OFF status even if it is located in an interlocked sec-
tion of the diagram.
In the following example, CIO 000200 will be turned ON when CIO 000002 is ON
and CIO 000003 is OFF. CIO 000200 will then remain ON until either CIO
000004 or CIO 000005 turns ON. With KEEP, as with all instructions requiring
more than one instruction line, the instruction lines are coded first before the
instruction that they control.
(011)
KEEP 000200
S: set input
R: reset input
Although the KEEP instruction can be used to create self-maintaining bits, it is
sometimes necessary to create self-maintaining bits in another way so that they
can be turned OFF when in an interlocked section of a program.
To create a self-maintaining bit, the operand bit of an OUTPUT instruction is
used as a condition for the same OUTPUT instruction in an OR setup so that the
operand bit of the OUTPUT instruction will remain ON or OFF until changes oc-
cur in other bits. At least one other condition is used just before the OUTPUT
instruction to function as a reset. Without this reset, there would be no way to
control the operand bit of the OUTPUT instruction.
The above diagram for the KEEP instruction can be rewritten as shown below.
The only difference in these diagrams would be their operation in an interlocked
program section when the execution condition for the INTERLOCK instruction
was ON. Here, just as in the same diagram using the KEEP instruction, two reset
bits are used, i.e., CIO 000200 can be turned OFF by turning ON either
CIO 000004 or CIO 000005.
0000 0000
04 05
Address Instruction
00000 LD
00001 AND NOT
00002 LD
00003 OR
00004 KEEP(011)
0002 Address Instruction
00
00000 LD
00001 AND NOT
00002 OR
00003 AND NOT
00004 AND NOT
00005 OUT
Section 4-7
Operands
000002
000003
000004
000005
000200
Operands
000200
000003
000000
000004
000005
000200