Background Execution - Omron SYSMAC CS/CJ Series Programming Manual

Cycle Time/High-speed Processing

6-1-10 Background Execution

Applications
Procedure
1,2,3...
244
The equation for maximum data link I/O response time is as follows:
Input ON delay
Cycle time of PLC at CPU Unit #1 × 1.5
Communications cycle time × 2
Cycle time of PLC at CPU Unit #2 × 1
Output ON delay
Total (data link I/O response time)
Background execution can be used to reduce fluctuations in the cycle time.
Background execution is supported only by CS1-H, CJ1-H, or CJ1M CPU
Units.
Table data processing (such as data searches) and text string processing
(such as text string searches), require time to execute, and can create large
fluctuations in the cycle time due to the extended amount of time required to
execute them.
With the CS1-H, CJ1-H, or CJ1M CPU Units, however, background execution
(time slicing) can be used to execute the following instructions over several
cycles to help control fluctuations in the cycle time. The PLC Setup enables
setting background execution for each type of instruction.
• Table data processing instructions
• Text string processing instructions
• Data shift instructions (ASYNCHRONOUS SHIFT REGISTER only)
Setting background execution for the above instructions can help control tem-
porary increases in the cycle time.
CS1 CPU Unit
MAX
Long execution
time
↓
Longer cycle time
when MAX is
executed.
Background execution can be used for large quantities of data processing,
such as data compilation or processing, that is required only at special times
(e.g., once a day) when reducing the effect on the cycle time is more impor-
tant than the speed of the data processing.
1. Set the PLC Setup to enable background execution for the required in-
structions.
2. Set the communications port number (logical port number) to be used for
background execution in the PLC Setup. This port number will be used for
all instructions processed in the background.
Note One port is used for all background execution. Background execu-
tion for an instruction can thus not be started if background execution
is already being performed for another instruction. Use the Commu-
nications Port Enabled Flag to control instructions specified for back-
1.5 ms
25 ms × 1.5
10 ms × 2
20 ms × 1
15 ms
94 ms
CS1-H or CJ1-H
Background
CPU Unit
execution
MAX
Execution
only
started.
Section 6-1
---
Faster by 12.5 ms
(25 ms x 0.5)
---
Faster by 20 ms
(20 ms x 1)
---
Faster by 32.5 ms
(26% faster)
Executed over
several cycles
using time slicing.