IAI MSEL, Instruction Manual, Page: 18 / 234

10
6. Transference of PIO Signal between Controllers
Please note the following when conducting transference of PIO signal between controllers.
To certainly transfer the signal between controllers with different scan time, it is necessary to
have longer scan time than the one longer than the other controller. To ensure to end the
process safely, it is recommended to have the timer setting more than twice as long as the
longer scan time at least.
● Operation Image
Also, if one tries to read the signal that is being re-written by the other, the signal may be read
wrongly.
Make sure to read the signal after the rewriting is complete. (It is recommended to have more
than 2 scan periods to wait.) Make sure not to have the output side to change the output until
the other side completes the reading. Also, a setting is made on the input area not to receive
the signal less than a certain time to prevent a wrong reading of noise. This duration also
needs to be considered.
Note 1 Because this controller performs two or more processing works including program
execution and error processing, in addition to I/O processing, the scan time in not
fixed.
7. PLC Timer Setting (Reference)
Do not have the PLC timer setting to be done with the minimum setting.
Setting to “1” for 100msec timer turns ON at the timing from 0 to 100msec while 10msec timer
from 0 to 10msec for some PLC.
Therefore, the same process as when the timer is not set is held and may cause a failure.
Set “2” as the minimum value for the setting of 10msec timer and when setting to 100msec,
use 10msec timer and set to “10”.
As shown in the diagram, the input and
output timings of two devices that have
different scan time do not match, of
course, when transferring a signal.
There is no guarantee that PLC would
read the signal as soon as this controller
signal turns on.
In such a case, make the setting to read
the signal after a certain time that is
longer than the longer scan time to
ensure the reading process to succeed on
the PLC side.
It is the same in the case this controller
side reads the signal.
In such a case, it is recommended to
ensure 2 to 4 times of the scan time for
the timer setting margin.
It is risky to have the setting below the
scan time since the timer is also
processed in the scan process.
In the diagram, PLC can only read the
input once in 20msec even though this
controller output once in some msec.
Because PLC only conducts output
process once in 20msec, this controller
identifies the same output status for that
while.
This controller
(scan time some msec)
(Note 1)
PLC
(e.g. scan time is 20msec)
Output
Process
Input
Process