Constant Scan Time - IDEC FT1A Series User Manual

Constant Scan Time

The scan time may vary whether basic and advanced instructions/FB are executed or not depending on input conditions to these
instructions/FBs. The scan time can be made constant by entering a required scan time preset value into special data register
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 to 1,000ms.
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.
Note: R/W is the abbreviation for read/write. When R/W, it can be read and written. When R, it can only be read. When W, it can only be written.
D8022
D8023
D8024
D8025
Example: Constant Scan Time
This example sets the scan time to a constant value of 500 ms.
MOV(W)
M8120
Constant Scan Time Preset Value (1 to 1,000ms)
Scan Time Current Value (ms)
Scan Time Maximum Value (ms)
Scan Time Minimum Value (ms)
S1 – D1 – REP
500 D8022
S AXIS P
MART
M8120 is the initialize pulse special internal relay.
When the SmartAXIS starts operation, the MOV (move) instruction stores 500 to special
data register D8022.
The scan time is set to a constant value of 500ms.
/L U ' M FT9Y-B1378
RO ITE SER S ANUAL
5: S F
PECIAL UNCTIONS
5-67