94
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 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 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 REG-
ISTER instruction (SFT(10)). An example of the use of work words and bits
with the SHIFT REGISTER instruction is provided in
5-13-1 SHIFT REGIS-
TER – SFT(10)
.
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. Under-
standing 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
following example, IR 00000, IR 00001, IR 00002, and IR 00003 are com-
bined in a logic block that stores the resulting execution condition as the sta-
tus of IR 24600. IR 24600 is then combined with various other conditions to
determine output conditions for IR 00100, IR 00101, and IR 00102, i.e., to
turn the outputs allocated to these bits ON or OFF.
00000
00003
00001
00004
00002
00005
00004
00007
00006
00005
24600
24600
24600
24600
00100
00101
00102
Address
Instruction
Operands
00000
LD
00000
00001
AND NOT
00001
00002
OR
00002
00003
OR NOT
00003
00004
OUT
24600
00005
LD
24600
00006
AND
00004
00007
AND NOT
00005
00008
OUT
00100
00009
LD
24600
00010
OR NOT
00004
00011
AND
00005
00012
OUT
00101
00013
LD NOT
24600
00014
OR
00006
00015
OR
00007
00016
OUT
00102
Differentiated Conditions
Work bits can also be used if differential treatment is necessary for some, but
not all, of the conditions required for execution of an instruction. In this exam-
Reducing Complex
Conditions
Work Bits
Section 4-8
