Intermediate Instructions; Work Bits (Internal Relays) - Omron SYSMAC CVM1 Series Operation Manual

Work Bits (Internal Relays)

4-8

Intermediate Instructions

4-9

Work Bits (Internal Relays)

Work Bit Applications
There are some instructions that can appear on instructions lines with conditions
to help determine the execution conditions for other instructions. These instruc-
tions are called intermediate instructions. Intermediate instructions cannot be
placed next to the right bus bar, only between conditions or between a condition
and a right-hand instruction. The four instructions shown below, NOT(010),
CMP(020), CMPL(021), and EQU(025), are intermediate instructions, and are
described in Section 5 Instruction Set. The input comparison instructions de-
scribed in 5-16-7 Input Comparison Instructions are also intermediate instruc-
tions.
(010)
NOT
(020)
CMP Cp1 Cp2
(021)
CMPL Cp1 Cp2
(025)
EQU Cp1 Cp2
In programming, combining conditions to directly produce execution conditions
is often extremely difficult. These difficulties are easily overcome, however, by
using certain bits to trigger other instructions indirectly. Such programming is
achieved by using work bits. Sometimes entire words are required for these pur-
poses. These words are referred to as work words.
Work bits are not transferred to or from the PC. They are bits selected by the
programmer to facilitate programming as described above. I/O bits and other
dedicated bits cannot be used as works bits. All bits in the I/O Memory that are
not allocated as I/O bits are available for use as work bits. Be careful to keep an
accurate record of how and where you use work bits. This helps in program plan-
ning and writing, and also aids in debugging operations.
Examples given later in this subsection show two of the most common ways
to employ work bits. These should act as a guide to the almost limitless num-
ber of ways in which the work bits can be used. Whenever difficulties arise in
programming a control action, consideration should be given to work bits and
how they might be used to simplify programming.
Work bits are often used with instructions that control bit status. The work bit is
used first as the operand for one of these instructions so that later it can be used
as a condition that will determine how other instructions will be executed. Work
bits can also be used with other instructions, e.g., with the SHIFT REGISTER
instruction (SFT(050)). An example of the use of work words and bits with the
SHIFT REGISTER instruction is provided in 5-14-1 SHIFT REGISTER –
SFT(050).
Although they are not always specifically referred to as work bits, many of the
bits used in the examples in Section 5 Instruction Set use work bits. Understand-
ing the use of these bits is essential to effective programming.
Section 4-9
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