Fixed Scan TimeCPU Scan Percentage The logic time includes the logic features and display and the display features (screen display, touch panel processing, communication). The logic feature runs the logic programs.
There are two scan modes for the display unit; a fixed scan time mode and a CPU scan percentage mode.
Fixed Scan Time
CPU Scan Percentage
Communicating via Ethernet or MPI may affect the scan time. See the following for more details.
30.16.1 Scan Time Delay
Scan time includes errors.
Updating the device/PLC addresses depends on Address Refresh, and is not affected by the fixed scan time or CPU scan percentage.
For details on address refresh, refer to 30.14.3.3 Address Refresh.
Logic time on the LT4000 Series is affected by the CANopen communication load. Therefore, when CANopen is set, logic time will be longer compared to when CANopen is not set.
This mode maintains the specified scan time.
It allows you to process a logic program in a certain cycle. Suitable for programs that prioritize control (logic programs) and for which the screen is mainly used for monitoring (data display) with few operations required.
Display Processing Time = Setup value for Fixed Scan Time (ms) minus Logic Time
For example, when 50 ms is the fixed scan time, and the logic execution time is 20 ms
Display Processing Time = 50 ms - 20 ms = 30 ms
As the logic time becomes longer, the processing time becomes shorter. For this reason, the display update speed on the display unit becomes slower; however, the logic program runs continuously.
The minimum scan time setting is 10 ms.
For the scan setting, input 10 ms or larger by 1 ms increments.
The scan time is automatically adjusted when the relationship between the logic time and fixed scan time is as follows.
Model |
Conditions when the Scan Time is automatically adjusted |
Examples of the Automatic Adjustment of Scan Time |
GP-3300 Series LT3000 Series |
When the Logic Time exceeds the Fixed Scan Time of 30%, the scan time is adjusted to "Logic Time divided by 0.3". |
Scan time is adjusted to 100 milliseconds. |
GP-3400 Series GP-3500 Series GP-3600 Series GP-3700 Series LT4000 Series SP5000 Series |
When the Logic Time exceeds the Fixed Scan Time of 50%, the scan time is adjusted to "Logic Time divided by 0.5". |
Scan time is adjusted to 60 milliseconds. |
Adjust the setting time based on the #L_AvgScanTime value after testing the operation on the display unit.
A.2 System Variable
This mode specifies the CPU percentage reserved for logic, and adjusts the scan time accordingly.
The mode prevents pressure on the display processing time caused by increased logic time, and it is suitable for systems that prioritize speed in screen operations and screen switching.
Scan Time = Logic Time / Setup Value of the CPU Scan Percentage (%)
For example, if 40% is specified as the CPU scan percentage and the logic execution time is 20 ms
Scan Time = (20 / 40) x 100 = 50 ms
Display Processing Time = 50 ms - 20 ms = 30 ms
As the logic time becomes longer, the display processing time and the scan time become longer. For this reason, as the logic time becomes longer, the time allocated for the display processing becomes longer. This results in improved display update speed on the display unit while slowing down the processing cycle of the logic programs.
Specify the scan time value for the CPU scan percentage by 1 ms increments.
The processing time per instruction in the logic program remains unchanged.
You cannot specify more than 50% for the CPU scan percentage.
If you specify 50% for the CPU scan percentage, the display processing time and logic program processing time will be the same. The display processing will not be prioritized.
Setup Procedure
Please refer to the Settings Guide for details.
5.4.5 System Settings [Display Unit] - [Logic] Settings Guide
From the [Project] menu, point to [System Settings], click [Display Unit] and open the [Logic] tab.
From the [System Settings] area, select [Fixed Scan Time] or [CPU Scan Percentage] and enter a setting value.
