6-5
Section
Work Bits (Internal Relays)
357
Work Bit Applications
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 number of
ways in which the work bits can be used. Whenever difficulties arise in program-
ming 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 the OUTPUT, OUTPUT NOT, DIFFERENTIATE
UP, DIFFERENTIATE DOWN, and KEEP instructions. 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(10)). An example of the use of work words and bits with the
SHIFT REGISTER instruction is provided in
7-16-1 SHIFT REGISTER –
SFT(10)
.
Although they are not always specifically referred to as work bits, many of the
bits used in the examples in
Section 7 Instruction Set
use work bits. Understand-
ing the use of these bits is essential to effective programming.
Work bits can be used to simplify programming when a certain combination of
conditions is repeatedly used in combination with other conditions. In the follow-
ing example, IR 00000, IR 00001, IR 00002, and IR 00003 are combined in a
logic block that stores the resulting execution condition as the status of
IR 21600. IR 21600 is then combined with various other conditions to determine
output conditions for IR 20000, IR 20001, and IR 20002, i.e., to turn the outputs
allocated to these bits ON or OFF.
00000
00003
00001
00004
00002
00005
00004
00007
00006
00005
21600
21600
21600
21600
20000
20001
20002
Address
Instruction
Operands
00000
LD
00000
00001
AND NOT
00001
00002
OR
00002
00003
OR NOT
00003
00004
OUT
21600
00005
LD
21600
00006
AND
00004
00007
AND NOT
00005
00008
OUT
20000
00009
LD
21600
00010
OR NOT
00004
00011
AND
00005
00012
OUT
20001
00013
LD NOT
21600
00014
OR
00006
00015
OR
00007
00016
OUT
20002
Reducing Complex
Conditions