6.
DATA COMMUNICATIONS
USING
AN
M
:
N
MULTIDROP
LINK
'3'
MELSEC-A
(1)
A
slave station that requires data communications with a PC CPU
transmits
a
communications request to obtain the access right to the
master station.
An example
of
the message format is shown in
(2)
below.
(2)
The master station transmits an approval response to the slave station
that made the communications request.
(An example of data communications using dedicated protocol
1)
+
:
Computer with the access right
'1
F([
number
87H)
-T-
I
(3)
After performing data communications with
a
PC CPU within the maxi-
mum data communications time set among computers, the slave station
that received an approval response executes the processing as shown
in
(5)
below.
(4)
The master station that transmitted the approval response and the slave
stations that do not have the access right check the access right time
of
the slave station that obtains the access right, and, ignore received
data which is addressed to other stations.
If
the access right time of a computer with the access right exceeds the
maximum data communications time, each computer executes the
processing mentioned
in
(7).
6-9
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