IAI Rec, Instruction Manual, Page: 17 / 158

Precautions for Handling
ME0394-1A
Intro-9
5. Creation of sequence programs
When creating a sequence program, be careful of the following.
If exchanging data between devices with different scan time, the length of time required for a
reliable signal reading process is greater than the longer scan time. (In order to safely perform
the reading process on the PLC side, we recommend using a timer set value of at least twice
the longer scan time.)
● Operational image
As shown in the diagram, if exchanging data
between 2 devices with different scan time,
obviously the I/O timing will not match.
When the signal of this controller turns ON, there
is no guarantee that the PLC will read it
immediately.
In cases like this, in order to achieve reliable
reading, set the PLC side to read after a period
greater than the longer scan time has passed.
This also applies when the reading is performed
on the controller side.
On this occasion, make sure the safety factor of
the timer setting is 2 to 4 times or more of the
scan time.
As the timer is also processed within the scanning
process, setting below the scan time is
dangerous.
The example shown in the diagram indicates that
even if this controller performs output process
once every 1 ms, the PLC can only recognize
once every 20 ms.
The PLC only performs the output process once
every 20 ms, meaning that it keeps recognizing
the same output status for that period.
Also, if reading is performed while the other device is rewriting output, incorrect signals may be read
at times. Wait until the rewriting is completely finished (allow interval of 2 scans or more), then
perform reading. In terms of the output-side device, do not allow its output to change until the other
device finishes the reading. Additionally, an input constant is set for the input component to prevent
mistaken detection of noise, etc. so it only accepts signals that last more than a certain period of
time. It is necessary to add this period of time as well.
This controller
(Scan time 1 ms)
PLC
(For example, scan time 20 ms)
Output
Process
Input
Process