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Calculations The equation for the cycle time from above is as follows:
Cycle time = Overseeing time + Program execution time + I/O refresh time +
Peripheral device servicing time
Process Calculation With Peripheral
Device
Without
Peripheral Device
Overseeing Fixed 0.7 ms 0.7 ms
Program execution 0.47 µs/instruction
× 5,000
instructions
2.35 ms 2.35 ms
I/O refresh See below. 0.34 ms 0.34 ms
Peripheral device
servicing
Minimum time 0.26 ms 0.0 ms
Cycle time Total of above 3.65 ms 3.39 ms
The I/O refresh time would be as follows for two16-point Input Units, four 8-point
Input Units, two 12-point Output Units (12-point Units are treated as 16-point
Units), and five 8-point Output Units controlled by the PC:
8 pts
(16 pts x 2) + (8 pts x 4)
x 20 µs = 0.34 ms
x 20 µs +
8 pts
(16 pts x 2) + (8 pts x 5)
6-2-2 PC with Link Units
Here, the cycle time is computed for a PC with a CPU21-E or CPU23-E CPU that
has a Memory Unit with a clock function installed. The PC configuration for this
could be as shown below.
The CPU controls three 8-point Input Units, three 8-point Output Units, a Host
Link Unit, and a Remote I/O Master Unit connected to a Remote I/O Slave Rack
containing four 16-point Input Units and four 12-point Output Units.
It is assumed that the program contains 5,000 instructions requiring an average
of 0.47 µs each to execute, and that nothing is connected to the RS-232C port
and no SYSMAC NET/SYSMAC LINK Unit is mounted.
Computer
Slave Rack
Host Link Unit
Remote I/O
Master Unit
CPU Rack
8-point
Input Units
8-point
Output Units
12-point
Output Units
16-point
Input Units
Calculating Cycle Time Section 6-2