5 I/O Refreshing
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NX-series Digital I/O Unit User’s Manual (W521)
z Slave Terminal Operation
The following describes the operation of Free-Run refreshing for Slave Terminals.
• The Communications Coupler Unit performs I/O refreshing for NX Units. (Refer to (a) in the figure
below.)
• The NX Units read inputs or refresh outputs at the time of I/O refreshing. (Refer to (b) in the figure
below.)
• The Communications Coupler Unit can read the most recent input value at the time of I/O refresh-
ing and the NX Units can control the most recent output value at the time of I/O refreshing. How-
ever, the timing to read inputs or to refresh outputs for each NX Unit in the Slave Terminal does
not occur at the same time. (Refer to (c) in the figure below.)
• The interval of I/O refreshing varies with the processing conditions of the Communications Cou-
pler Unit or the host communications master. Therefore, the interval of the timing to read inputs or
to refresh outputs for NX Unit is not always the same. (Refer to (d) in the figure below.)
• In order to read input values correctly, you must set the inputs before the total of the ON/OFF
response time and the input filter time from the timing to read inputs for each NX Unit.
• The ON/OFF response time is required from when outputs are updated until the output status is
set on the external terminals of the NX Units.
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