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4-6. Communication Times
Maximum Data Transfer Response Time “Maximum Rdt”
The maximum amount duration of time needed from the point when a data transfer command message is trans-
ferred from one station to the point when the response message is sent back to the original station is calculated as
follows :
Ttc
Command
message
Response
message
Command
message
Response
message
Approx. 2-scan time
2TscB
Ttc
T
stA
T
stB
I/O update
Buffer update
Data transfer
Station A
(UNIT NO. A)
CPU scan
Buffer
Transmission
cycle
Station B
(UNIT NO. B)
Buffer
CPU scan
Maximum Rdt = Ttc + TscB + TscB + Ttc + TscA
where :
Ttc
= Time needed for one transmission cycle
TscA = Scan time of Programmable Controller “A”.
TscB = Scan time of Programmable Controller “B”.
