Omron NJ-series User Manual page 168

The values of the constants a to d in above equation vary depending on the type of the CPU Unit.
CPU Unit model
NJ501- 
NJ301- 
 Setting Variable Access Time
Set the variable access time in the Task Settings Tab Page displayed by selecting Configurations
and Setup  Task Settings on the Sysmac Studio. The setting must be made for each task by
entering the ratio to the task period. The default value is 3%. For the details on the settings, refer to
the Sysmac Studio Version 1 Operation Manual (Cat. No. W504).
 Example of Variable Access Time Setting
The following is an example of variable access time setting.
In this example, it is assumed that there are the following three variable accesses from outside the
Controller to the task that operates in the NJ501- CPU Units.
Access No.
1
2
3
Using the equation, the variable access time for Access No.1 is calculated as follows.
Variable access time for Access No.1 = 600 * 0.001 + 8 * 0.58 + 1 * 1.41 + 6.68
In the same way, you can calculate the access time for the other accesses and get the following val-
ues.
Access No.
1
2
3
If only one of these accesses occurs in one task period, you set the Variable Access Time to the one
for Access No.1, which requires the longest access time.
The variable access time for Access No.1 is 13.33 µs. Therefore, when the task period is 500 µs, the
Variable Access Time is set to 13.33/500  3%.
If every access occurs once in one task period, the Variable Access Time is calculated with the
equation as follows.
Variable access time
When the task period is 500 µs, the Variable Access Time is set to 20.25/500  5%.
NJ-series CPU Unit Software User's Manual (W501)
a
0.001
0.0009
Source of variable access
EtherNet/IP tag data link
EtherNet/IP tag data link
CIP communications instruction
= 13.33 [µs]
Variable Access Time [µs]
13.33
10.61
= (600 + 200 + 1000) * 0.001 + (8 + 4 + 1) * 0.58 + (1 + 1 + 1) * 1.41 + 6.68
= 20.25 [µs]
Constant value [µs]
b c
0.58 1.41
1.03 2.15
Total size of vari-
Number of vari-
ables to access
ables to access
[bytes]
600
200
1,000
9.67
5 Designing Tasks
d
6.68
7.52
Number of
accesses
8 1
4 1
1 1
5-41
5