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Terminology
NX-series NX1P2 CPU Unit Hardware User’s Manual (W578)
PDO communications
An abbreviation for process data communications. Data is exchanged between the
master and slaves on a process data communications cycle. (The process data com-
munications cycle is the same as the task period of the primary periodic task.)
periodic task A task for which user program execution and I/O refreshing are performed each
period.
PLC Function Module One of the function modules. This function module executes the user program,
sends commands to the Motion Control Function Module, and provides an interface
to the USB and SD Memory Card.
POU An acronym for “program organization unit.” A POU is a unit in a program execution
model that is defined in IEC 61131-3.
A POU contains an algorithm and a local variable table and forms the basic unit
used to build a user program.
There are three types of POUs: programs, functions, and function blocks.
primary periodic task The task with the highest priority.
process data communications One type of EtherCAT communications in which process data objects (PDOs) are
used to exchange information cyclically and in realtime. Process data communica-
tions are also called PDO communications.
program Along with functions and function blocks, one of the three types of POUs.
Programs are assigned to tasks to execute them.
Range Specification One of the variable specifications. You can specify a range for a variable in
advance. The variable can take only values that are in the specified range.
Retain One of the attributes of a variable. The values of variables with a Retain attribute
are held at the following times. (Variables without a Retain attribute are set to their
initial values.)
• When power is turned ON after power interruption
• When the CPU Unit changes to RUN mode
• When you specify to not initialize the values when the user program is transferred
SDO communications One type of EtherCAT communications in which service data objects (SDOs) are
used to transmit information whenever required.
Servo Drive/encoder input slave Any of the EtherCAT slaves that is assigned to an axis. In the NJ/NX-series Sys-
tem, it would be a Servo Drive or Encoder Input Slave Unit.
slave A device that performs remote I/O for a master.
slave and Unit configurations A generic term for the EtherCAT configuration and Unit configuration.
Slave Terminal A building-block remote I/O terminal to which a Communications Coupler Unit and
NX Units are mounted. A Slave Terminal is one type of slave.
Special Unit Setup A generic term for the settings for a Special Unit, including the settings in allocated
DM Area words.
structure One of the derivative data types. It consists of multiple data types placed together
into a layered structure.
synchronization A function that automatically compares the information in the NJ/NX-series Control-
ler with the information in the Sysmac Studio, displays any differences and loca-
tions in a hierarchical form, and can be used to synchronize the information.
Sysmac Studio A computer software application for setting, programming, debugging, and trouble-
shooting NJ/NX-series Controllers. It also provides operations for motion control
and a Simulator.
system common processing System processing that is performed by the CPU Unit to perform I/O refreshing and
the user program execution within a task. Exclusive control of variables between
tasks, data trace processing, and other processing is performed.
system service Processing that is performed by the CPU Unit in unused time between task pro-
cessing. The system service includes communications processing, SD Memory
Card access processing, self-diagnosis processing, and other processing.
system-defined variable A variable for which all attributes are defined by the system and cannot be changed
by the user.
task An attribute that defines when a program is executed.
task period The interval at which the primary periodic task or a periodic task is executed.
Term Description
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