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424
ing into account such things as the number of I/O points, the programming
instructions used, and whether or not Programming Devices are being used.
This section shows a basic example of cycle time calculation. Operating
times are given in the tables in 6-2 Cycle Time.
Here, we’ll compute the cycle time for a CVM1D controlling only I/O Units,
five on the CPU Rack and ten on an Expansion I/O Rack. The PC configura-
tion for this is shown below. It is assumed that the program contains 20,000
instructions requiring an average of 0.3
µ
s each to execute.
Refer to the next section for instruction execution times. Using the cycle time
in calculating the I/O response time is described in the last part of Section 6.
16-point Input
Units
32-point Input
Units
16-point Output
Units
CPU Rack
Expansion I/O Rack
32-point Output
Units
The following table shows the time required for each process in the cycle.
Process
Calculation
Time (ms)
1
Overseeing time
(basic processes)
---
8.5
2
Program execution
20,000 steps
×
0.3
µ
s
6.0
3
Output refreshing
[(16 points
×
2 + 32 points
×
5)
÷
16]
×
7
µ
s
0.084
4
Input refreshing
[(16 points
×
3 + 32 points
×
5)
÷
16]
×
8
µ
s
0.104
5
I/O bus check
---
1.2
6
Duplex refreshing
[(16 points
×
3 + 32 points
×
5)
÷
16]
×
10
µ
s
0.11
Approximate cycle time (processes 1 through 5)
16.00
Calculations
Calculating Cycle Time
Section 6-3
Summary of Contents for CVM1D
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