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In looking at the following timing charts, it is important to remember the se-
quence in which processing occurs during the PC scan, particular that inputs will
not produce programmed actions until the program has been executed.
When calculating the response times involving inputs and outputs from another
CPU Unit connected by an I/O Link Unit, the cycle time of the controlling CPU
Unit and the cycle time of the PC to which the I/O Link Unit is mounted must both
be considered.
Caution Noise may increase I/O delays.
The remote I/O transmission time is computed as follows:
T
RM = Total Slave transmission time for one Master
= ΣTRT + ΣTTT
TRT = Transmission time for each Slave
= 1.4 ms + (0.2 ms × n)
Where n = number of I/O words on the Slave Rack
TTT = Optical I/O Unit/I/O Terminal transmission time
= 2 ms × m
Where m = number of Optical I/O Units/I/O Terminals
The minimum response time occurs when all signals are processed as soon as
they are received. Here, three scans are required so that the program is
executed, as shown in the following diagram.
Time = Input ON delay + cycle time × 3 + output ON delay
Cycle time > Remote I/O transmission times
Cycle time
CPU Unit
Master
Slave
Input
Output
Program execution
Transfer to CPU Unit
Transfer to Master
Slave I/O refresh
Remote I/O Transmission
Times
Minimum I/O Response
Time
I/O Response Time Section 6-4