IDEC MicroSmart - Manual (Page 147)

5: S PECIAL F UNCTIONS
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Constant Scan Time
The scan time may vary whether basic and advanced instructions are executed or not depending on input conditions to
these instructions. The scan time can be made constant by entering a required scan time preset value into special data reg-
ister D8022 reserved for constant scan time. When performing accurate repetitive control, make the scan time constant
using this function. The constant scan time preset value can be between 1 and 1,000 ms.
The scan time error is ±1 ms of the preset value normally. When the data link or other communication functions are used,
the scan time error may be increased to several milliseconds.
When the actual scan time is longer than the scan time preset value, the scan time cannot be reduced to the constant value.
Special Data Registers for Scan Time
In addition to D8022, three more special data registers are reserved to indicate current, maximum, and minimum scan time
values.
Example: Constant Scan Time
This example sets the scan time to a constant value of 500 ms.
D8022 Constant Scan Time Preset Value (1 to 1,000 ms)
D8023 Scan Time Current Value (ms)
D8024 Scan Time Maximum Value (ms)
D8025 Scan Time Minimum Value (ms)
M8120
REP
M8120 is the initialize pulse special internal relay.
When the CPU star ts operation, the MOV (move) instruction stores 500 to
special data register D8022.
The scan time is set to a constant value of 500 ms.
S1 –
500
D1 –
D8022
MOV(W)