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MELSEC-Q
4 THE EXCHANGE BETWEEN THE PLC AND BUFFER MEMORY
4.2.2 PLC station number
In AD51H-BASIC, not only can the PLC attached to the communication module be
accessed, but PLCs of other stations that are data-linked via the MELSECNET can be
accessed as well. However, the following restrictions apply depending on whether the
PLC with the communication module attached is a master station (control station) or
local station (standard station).
(1) MELSECNET (II), MELSECNET/B
(a) When the CPU with the communication module attached (self station) is a
MELSEC two-tier master station, data from all local stations and remote I/O
stations within the self station and two-tier loop can be accessed.
Only the buffer memory of the special function module can be accessed for
remote I/O stations.
Local Station #1
(self station)
(Master
Station)
Communication
module
(Local Station #1)
(Local Station #2)
Remote Station #2
Local Station #3
Master Station
The names in
parentheses are
station names
under a three-tier
system.
(b) When the CPU with the communication module attached (self station) is a
MELSEC two-tier or three-tier local station, only the data from the self
station and master stations within the same loop can be accessed.
Local Station #1
Self
station
(Master
Station)
Communication
Module
(Local Station #1)
(Local Station #2)
Remote Station #2
Master Station
Local Station #1
self station
(Master
Station)
(Local Station #2)
Remote Station #2
Local Station #3
Master Station
Local Station #3
Communication Module
Local Station #1
The names in
parentheses are
station names
under a three-tier
system.
The names in
parentheses are
station names
under a three-tier
system.
