I
PROGRAMMING
I
Y20
Y20
~~
Hl-
0-
Load
I
Load
I
0-
M51
............................
I
II
I
Sequence program
Output circuit (external devices)
IAuxiliary relays
M,
L,
S
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There are three types of auxiliary relays available for use in the PLC sequence
program, internal relays
(M),
latch relays (L), and step relays
(S).
There is no limit
to
the number of NIO and NIC contacts used within a program.
The internal relays
(M)
and step relays
(S)
cannot be latched and therefore all of
them are switched
OFF,
if the PLC is switched ON, reset or latch cleared. The latch
relays are battery backed and therefore they retain the last operation state when the
PLC is turned ON or reset.
To
switch
OFF
all
of
the latch relays, use the latch clear
function of the PLC.
I
Link
relavs
B
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The link relays
(B)
are used as internal relays for the data link system. The ONIOFF
data of the link relays used within the data link system can be read by switching
them ON/OFF as output coils in the host or master station and used as contacts in
all of the stations on the data link system. The link relays therefore allow ONlOFF
data
to
be transferred between the master and local stations.
The range of link relays for use as coils in each station must be set in the
parameters
of
the master station. Link relays which are not being used for the data
link system can be used as internal relays. There
is
no restriction
to
the number of
NIO contacts and NIC contacts of the link relays used in a sequence program.
59
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