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6.
DATA COMMUNICATIONS USING AN M : N MULTIDROP LINK
MELSEC-A
(3) Each computer without the access right checks the access right time
(the maximum data communications time) of the computer with the
access right and ignores incoming data which is addressed to others.
When the access right time exceeds the maximum data communica-
tions time, each computer executes the processing mentioned in
(7).
+:
Computer with the access right
(4)
The computerthat has finished data communications with PC CPUs and
the computers that do not need data communications with PC CPUs
transmit the access right transfer data to the computer at the next
station number.
When a computer is unable to receive a response message from the
next computer to which the access right is to be transferred, it keeps
on transmitting the access right transfer data to the following com-
puters in the order of station numbers until the access right transfer is
completed.
(5) The computer to which the access right is given transmits a response
message to the computer that gave the access right.
(An example of data communications using dedicated protocol
1)
Computer to
which the access
right is transferred
(SOH)
Message mentioned in 4
.,
Message mentioned in 5
Computer that
transfersthe
access right
(SOHI
' 1
The command symbol
'ZZ' in this example is
indicated only for ex-
planation. Use any
.
desired symbol forthe
transfer command to
obtain the access right.
See Section
8.3
tells how
to read the message
format figure.
(6) The computer that transmitted a response message and obtained the
access right executes the processing mentioned in
(2).
;
0 %
I
From station
number
@OH!
38n13a(
I
TO station
number
181H)
3 8 n 1 3 1 H
I
122)
W I W
Message
wait ,ime
12)
3 %
I
Sum check
code
107W
4 2 H 1 3 7 t
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