Omron NJ501-1400 User Manual page 53

Axis Variable Update Timing
Axis Variables are system-defined variables for some of the axis parameters and for the monitor
information, such as the actual position and error information for the axes controlled by the MC
Function Module.
If you access an Axis Variable during the priority-16 periodic task, the values of the variable that
were read at the start of the periodic task are used.
Also, the values of an Axis Variable are not written when a motion control instruction (FB) is exe-
cuted. They are written in motion control processing (MC) at the start of the next periodic task.
Primary period
Primary
UPG
IO MC
periodic task
Values of
Priority-16
Axis
periodic task
Variable
*1
are read
*1 The values of an Axis Variable are read at the start of user program execution for the periodic task.
*2 The values of an Axis Variable are not written when a motion control instruction (FB) is executed in the periodic
task.
*3 The values are written during this motion control processing (MC).
Precautions for Correct Use Precautions for Correct Use
• When motion control instructions are placed in a periodic task, the response time of the Servo
Drive will increase if the task period of the periodic task is lengthened.
• Make sure that all axes can be stopped safely for emergency stops, including emergency
stops commanded from external devices.
• The execution timing of motion control instructions in a priority-16 periodic task is not the same
as the execution timing for I/O control. Design the user program to allow for this.
Additional Information
For information on Axis Variables, refer to 3-1-3 Introduction to Axis Variables.
NJ-series CPU Unit Motion Control User's Manual (W507)
UPG
IO MC
UPG UPG
FB
Execution of motion control instructions
Task period (primary period × 3)
2 Motion Control Configuration and Principles
I/O
OUT
UPG UPG
IO MC IO
*2
Servo
Execution
command
UPG
MC IO MC
*3
2
2-9