4-6. Communication Times
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3. Data Transfer Response Time
The Data Transfer Response time is the time bettween the point when a data transfer command message is
transferred from one station to the point when the response message is sent back to the original station.
Since the actual Data Transfer Response Time depends upon the transmission cycle time, the transmission timing
and the time needed for CPU processing(CPU scan time) etc., the Data Transfer Response Time will deviate
between the minimum and the maximum Data Transfer Response Times. When installing a network, these values
should also be taken into consideration.
Minimum Data Transfer Response Time “Minimum Rdt”
The minimum amount of time needed from the point when a data transfer command message is transferred from
one station to the point when the response message is sent back to the original station is calculated as follows :
Command
message
Response
message
Command
message
Response
message
Approx. one scan time
TscB
I/O update
Buffer update
Data transfer
T
stA
T
stB
One scan
Station A
(UNIT NO. A)
CPU scan
Buffer
Transmission
cycle
Station B
(UNIT NO. B)
Buffer
CPU scan
Minimum Rdt = TstA + TscB + TstB
where :
TstA =Time needed for the PC Link processing by station “A”.
TscB =Scan time of the Programmable Controller “B”.
TstB =Time needed for PC Link processing by station “B”.
