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Overview of 1:N NT Links Section 8-1
8-1 Overview of 1:N NT Links
A PLC can be connected to Programmable Terminals (PTs) using an RS-
232C or RS-422A/485 port. The I/O memory of the PLC is allocated as a Sta-
tus Control Area and a Status Notification Area for the PT, as well as to
objects, such as touch switches, lamps, and memory tables. This enables the
status of the I/O memory in the PLC to be controlled and monitored by opera-
tions from the PT, without the use of ladder programming in the PLC. One
PLC can be connected to up to eight PTs.
The user does not need to be aware of the 1:N NT Links commands. All that is
necessary is to allocate PLC memory for the PTs.
This section explains the Setup Area and the Protocol Status Flags when a
Serial Communications Board or Unit is used with 1:N NT Links. For details
on the operating PTs, refer to the operation manual for the PT.
Note 1. Set the serial port on the PT to a 1:N NT Link. The Serial Communications
Board or Unit will not be able to communicate if the PT port is set for a 1:1
NT Link. Connection is not possible to PTs that do not support 1:N NT
Links.
2. The number of PTs that can be connected to one port is limited by the CPU
Unit’s cycle time when a Serial Communications Board or Unit is used in a
1:N NT Link, as shown in the following diagrams. Although some commu-
nications will be possible even if these restrictions are exceeded, commu-
nications errors will occur depending on the PT operating conditions and
communications load. Always abide by these restrictions.
3. The Programming Console functions of the PT (Expansion Mode) cannot
be used when connected to Serial Communications Board or Unit ports.
They can be used only by connecting to the peripheral port or RS-232C
port on the CPU Unit.
4. Set a unique unit number for each PT connected to the same PLC. If the
same unit number is set for more than one PT, malfunctions will occur.
1:N NT Link
PT
NT Link
(Set to 1:N)
Serial Communications Board
(CS Series only)
Serial Communications Unit
(CS/CJ Series)
PT
Serial Communications Board
(CS Series only)
Serial Communications Unit
(CS/CJ Series)
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