Data Communications Between Programmable Controller Cpu And External Devices By Designating A Master Station And Slave Stations - Mitsubishi MELSEC L Series User Manual

14 DATA COMMUNICATIONS USING EXTERNAL DEVICE AND PROGRAMMABLE CONTROLLER CPU M : N CONFIGURATION
14.3.2 Data communications between programmable controller CPU and external devices
by designating a master station and slave stations
Master station
external device
Communications
Communications
request complete report
Slave station
external device 1
Slave station
external device 2
Slave station
external device m-1
Master station (Before 2))
External device
(Station No.:1B )
H
2)
(Station No.:0 )
H
CPU C24
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One of the external devices is made the master station and the other external devices
communicate data with the programmable controller CPU after obtaining permission
from the master station.
(Example)
Permission
granted
response
Communications
request
Response
Permission
granted
response
Data communications
with programmable
controller CPU
The following uses an example to describe the procedure when external devices
communicate data with the programmable controller CPU.
In this example, after the start of data communications between external devices and
the programmable controller CPU, the external devices perform a maximum data
communications time time-out check. Slave station external devices that are not
communicating data with the programmable controller CPU check if the external
device that completed data communications with the programmable controller CPU
transmitted a communications complete report.
In the following descriptions, the external device with the lowest station No. (1B
assumed to be the master station and the other external devices are assumed to be
slave stations.
: External device that obtained the line usage right
External device
(Station No.:1C
1)
(Station No.:1 )
H
CPU C24
TIme
General report to
start and end data
Communications
communications request
between master
station and
programmable
controller CPU
Start End
(after 2))
)
H
(Station No.:2 )
H
CPU C24
Communications
complete report
Permission
granted
Response
response
Data communications with programmable controller CPU
External device
(Station No.:1D ) (Station No.:1E
H
(Station No.:15
CPU
C24: Q series C24, QC24 (N), UC24
) is
H
External device
)
H
)
H
C24
14 - 9