4-6. Communication Times
52
Maximum P/W PC Link Response Time “Maximum Rpc”
The maximum 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 ;
Buffer update
I/O update
Approx. one scan time
TidA
TscB
Ttc
Station A
(UNIT NO. A)
Input transition
CPU scan
Buffer
Transmission
cycle
Station B
(UNIT NO. B)
CPU scan
Buffer
I/O update
Input delay
TscA
T2
TscB
Output delay
Buffer update
I/O update
T1
TodB
Output transition
Maximum Rpc = TidA + TscA + T1 + Ttc + TscB + T2 + TscB + TodB
where :
TidA
= Input delay time of the input transition at Programmable Controller “A”.
TscA
= Scan time at the Programmable Controller “A”.
T1
= Time needed between the I/O update and the W Type(Wire) Link Unit’s buffer update
Ttc
= (1 +
) x TscA
TscA
Ttc
= Time needed for one transmission cycle
TscB
= Scan time at the Programmable Controller “B”.
T2
= Time needed from the buffer update signal reception and the CPU memory update at
station “B”.
Ttc + Tsti max.
= (1 +
) x TscB
TscB
where ;
Tsti max.=Time needed for PC Link processing by station “i”.
Here, the Tsti max. is supposed to be the longest time needed for
processing by one station.
TodB
= Output delay time of the output transition from Programmable Controller station “B”
