5 I/O Refreshing
5 - 8
NX-series Analog I/O Units User’s Manual for Analog Input Units and Analog Output Units (W522)
The I/O refreshing methods that you can use depend on the model of the NX Unit. After you decide on
which I/O refreshing method to use, select the NX Units.
With this I/O refreshing method, the refresh cycle of the NX bus and I/O refresh cycles of the NX Units
are asynchronous.
NX Units read inputs or refresh outputs at the time of I/O refreshing.
This method is used when it is not necessary to be aware of factors such as the I/O timing jitter and the
concurrency of the timing to read inputs and refresh outputs between the NX Units.
The following describes the operation of Free-Run refreshing between the NX-series NX1P2 CPU Unit
and the NX Units.
• The CPU 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 CPU Unit can read the most recent input value at the I/O refreshing and the NX Units can control
with the most recent output value at the I/O refreshing. However, timing to read inputs or to refresh
outputs for each NX Unit 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 CPU Unit. 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.)
*1. Two types of time stamp refreshing are available: one is input refreshing with input changed time and the other
is output refreshing with specified time stamp.
*2. The EtherCAT Slave Terminal operates in DC Mode.
*3. The EtherCAT Slave Terminal operates in Free-Run Mode.
*4. Refer to the manuals for the specific NX Units for details on the operation when the DC is set to Disabled
(FreeRun).
5-2-3 Selecting NX Units
5-2-4 Free-Run Refreshing
Description of CPU Unit Operation
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