Rockwell Automation 1775-S4B,D17756.5.3 User Manual SCANNER/MSG HND - Manual (Page 132)

Chapter
12
12Ć1
Execution Time Considerations
After reading this chapter, you will be aware of the factors that affect
1775-S4B scanner execution time.
The 1775-S4B scanner can execute procedures of many commands,
operators, and functions. However, each command, operator, and function
takes a certain amount of time to execute. In some cases, a procedure
executes faster than the data transmits for printing. In other cases, the
execution time may be long enough to cause a delay between print items in
a procedure.
Obviously, one factor in execution time is the length of a procedure; the
longer the procedure, the longer the execution time. However, you should
also consider the following less obvious factors:
Active I/O channels
Address
complexity
Symbol order
Assignment values
Command line comments
We describe these factors in the following five sections.
The 1775-S4B scanner gives top priority to its four I/O channels. If any
I/O channels are active, the 1775-S4B scanner gives top priority to
scanning and processing I/O data.
You should also be aware that it takes several times longer to execute a
procedure while four I/O channels are active than while no I/O channels
are active.
If procedure execution speed is critical in your application, you can make
the unused I/O channels inactive in LIST to increase speed. Refer to
chapter 4 for detailed information on the LIST function.
You also might consider adding another 1775-S4A scanner to perform I/O
scans. This additional scanner could enable the 1775-S4B scanner to
execute procedures with all its I/O channels inactive.
12.0
Chapter Objectives
12.1
Introduction
12.2
Active I/O Channels