KEYENCE Visual KV Series - Manual (Page 27)

1.1 Before Creating Programs
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Chapter 1 Programming
1.1.2 Scan Time
Scan time
The Visual KV Series repeatedly executes a ladder based on the sequence circuit
as follows.
The duration of time required to perform one cycle is called the scan time (or cycle
time). The scan time varies based on program size and the instructions used in the
program.
Input response time delay
In addition to the I/O processing time, there is also an input time delay in the Visual
KV Series caused by the scan time. The input time delay is generated because the
input status can only be read during the input processing time. If the input status is
changed after input processing, the changed contents can only be read during the
next scan time.
In the figure below, 1 and 2 can be read but 3 cannot be read.
Reference: The maximum and minimum values of the input response time are as
follows.
Maximum value: Input time constant + Scan time x 2 + Output response delay time
Minimum value: Input time constant + Scan time + Output response delay time
Note 1: When the input time constant is made small by setting the HSP instruction,
special utility relay 2813, and data memory DM1940, a signal may not be received if
its ON time is shorter than the scan time.
Note 2: The INT instruction is independent of the scan time.
Note 3: The minimum scan time is 140 µs (with the basic unit).
Input processing
Writes the ON/OFF status of all input terminals to the input
memory before executing the program.
Program execution
Reads the ON/OFF status of each device (internal utility relay,
timer, counter, etc.) based on the instructions, and performs
arithmetic operations.
Writes the arithmetic operation result to the output memory.
Output processing
Outputs the contents of the output memory to output terminals.
ON
OFF
1 2 3
Input signal
Read Read
Output processing Input processing
Program
execution
Scan time
Output processing Input processing
Program
execution
Scan time
Output processing Input processing
Program
execution
Output processing Input processing
Program
execution
Output processing
Input processing
KVNKA Chap 01P.p65 08.3.11, 11:49 AM 3