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Communications with the Host Section 1-4
The words and bits allocated for direct connection are called the allocated
words and allocated bits.
The direct connection function allows the data to be displayed at the NT631/
NT631C to be read from the memory area in the PLC and written to memory
tables in the NT631/NT631C. Also, the data input at the NT631/NT631C can
be written to the memory area in the PLC. The NT631/NT631C screen can be
changed in accordance with statuses in the PLC memory area, and the
NT631/NT631C’s status data can be written to the PLC’s memory area.
Features of the Direct
Connection Function
The direct connection function has the following features.
• The bits and words referring to operating status and work instruction infor-
mation and those for storing input data can be freely allocated to almost
any area of the PLC memory.
• Since the NT631/NT631C can directly refer to PLC bit and word data with-
out using the program at the PLC, it can be connected to the PLC without
changing the PLC program which controls the currently running produc-
tion line.
• The area to control and provide notification of the NT631/NT631C status,
including display screens, display/no display status, and buzzer output,
can be freely allocated to any part of the PLC data area. This means that
the PLC status can be read and controlled just by reading this area at the
PLC side, without preparing a special communications program.
The direct connection function allows the NT631/NT631C to directly read and
write almost all bits and words in the PLC and to automatically change the
NT631/NT631C screen display. This function can reduce the load on the PLC
so that its program development efficiency is improved.
1-4-2 Host Link
The host is connected to a PT in a 1:1 connection, and the words and bits of
the host are read and displayed by host link communications. This method
can be used for connection to the majority of PLC types.
1-4-3 NT Link
NT link is a method for high-speed communications with a PLC using the
direct connection function. The PLCs that can be connected with the NT link
are as follows.
CPM1, CPM2A, CPM2C, CQM1, CQM1H, C200HS, C200HX/HG/
HE(-Z)E, CS1G/CS1H-E(V1), CS1D, CJ1G/CJ1H/CJ1M, CVM1/CV-series
PLC (-EV1 or later version), SRM1
Besides the 1:1 NT link method, in which one PLC is connected to one PT, the
NT631/NT631C can also use the 1:N connection NT link method, which
allows a maximum of eight PTs to be connected to one PLC port.
PLCs that can be connected with the 1:N connection NT Link method are as
follows: CQM1H, C200HX/HG/HE(-Z)E, CS1G/CS1H-E(V1), CS1D, CJ1G/
CJ1H/CJ1M.
PLC
NT631/NT631C
DM area I/O relay area
Auxiliary relay area Timers/counters