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323
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
µ
s/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
µ
s = 0.34 ms
x 20
µ
s +
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
µ
s 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