4-6. Communication Times
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Since the actual P/W PC Link Response Time depends upon the transmission cycle time, the transmission timing
and the time needed for CPU processing(CPU scan time) etc., the P/W PC Link Response Time will deviate
between the minimum and the maximum possible P/W PC Link Response Times. When installing the network,
these values should be taken into consideration.
Minimum P/W PC Link Response Time “Minimum Rpc”
The minimum amount of time needed between an input transition from a Programmable Controller and the
corresponding output transition to the next Programmable Controller is calculated as follows ;
Output delay
One scan
One Transmission cycle
Buffer update
I/O update
Approx. one scan time
Approx. one scan time
TidA
TscA
T
sti
T
stA
TodB
TscB
(UNIT NO. A)
Input transition
CPU scan
Buffer
Transmission cycle
Station B
(UNIT NO. B)
Output transition
CPU scan
Buffer
I/O update
Input delay
Minimum Rpc = TidA + TscA + TstA + Tsti min. + TscB + TodB
where :
TidA
= Input delay time of the input transition at Programmable Controller stationed as “A”.
TscA
= Scan time of the Programmable Controller “A”.
TstA
= Time needed for the PC Link processing by “A”.
Tsti min = Time needed for the PC Link processing by station “i”.
Here, the Tsti min. is supposed to be the shortest time needed for processing by one station.
TscB
= Scan time of Programmable Controller “B”.
TodB
= Output delay time for the output transition of Programmable Controller “B”.
