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6. DATA COMMUNICATIONS USING AN M
: N MULTIDROP LINK
MELSEC-A
6.3
Procedure for Data Communications with a PC CPU
This section explains the procedure for computer interlocking and data
communications with a PC CPU when constructing an m
:
n multidrop link.
{
6.3.1
Communications between each computer and PC CPUs
Each computer obtains the access right (one after another according to the
order of the station number of each computer) and then does data com-
munications with PC CPUs.
Example
Time
Computer
(station number 8 0 4
E 1 2 i
;
p
y
:
;
a
;
c
Computer
(station number 81
4
/
Data communications
with the PC CPU
Computer
(station number80H
+
(m
-
I))
I V
The following example shows the procedure for data communications
between each computer and PC CPUs.
+ :
Computer with the access right
Computer
When performing
data
computer
(station
communications wah
number
BOH)
a PCCPU
number 81H)
(station number 1H)
(
(station
number 87H)
number
88H)
I
I
W o n number OH)
I
(Station number tH)
(Station number2H)
CPU
I
Q4
I
CPU
C24
_
i
i
_
I
I
-
----1
L
--------,
(1)
When starting a system, the computer allocated with the minimum
station number (80H) obtains the access right.
(2) The computer which has the access right:
(a) Performs data communications with PC CPUs within the maximum
data communications time set among computers, and then, starts
procedure (4).
(b) Starts procedure (4) if
it
does not perform data communications
with PC CPUs.
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