Rockwell Automation 1771-KA2 Communication Adapter Module User Manual
Page 42
Commands
Chapter 4
4-6
This first restriction simply states that no bit should be directly controlled,
that is, addressed, by both an output instruction at its local station
processor and a bit write command from some remote station processor.
Bit write commands are generally used to set storage bits in a station
processor data table. These storage bits may then be examined in the user
program as conditions to energize an output bit. This indirect
programming technique allows control using bit write commands, but
helps to prevent the confusion that can result if an individual bit is
controlled from both an OUTPUT ENERGIZE instruction and a bit write
command.
Figure 4.3 gives an example of an indirect programming technique used to
control bit 01001, which is addressed by an output instruction, with a bit
write command. Here storage bit 12104 is controlled by the bit write
command. This bit is then examined by the program to control the status
of bit 01001. The output bit, 01001, cannot be directly addressed by the
bit write command. However, by controlling the storage bit and
examining it in the program, the same effect is achieved.
Figure 4.3
Bit Control Use (example)
12104
a. Original Rung
01001
11113
Input
Control of this output
Output
desired. However bit
already addressed by
output intructions
01001
11113
Input
Output
Storage Bit
Control bit through
bit write command to
control output 01001.
b. Recommended Technique