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The cycle time is the total of all these calculations.
1.6 ms + 0.51 ms + 4.43 ms = 6.54 ms
If a peripheral device had been present it would have been:
1.6 ms + 0.51 ms + 4.43 ms + 1 ms = 7.54 ms
Process Formula Peripheral device servicing (ms)
With Without
1. Overseeing
2. Input/output refreshing
3. Peripheral device servicing
4. Instruction execution
Fixed
0.29 + 0.07 * (1–1)
((1) + (3) + (4)) * 0.05 = 0.3 < 1
14.75 * 300
1.6
0.51
1.00
4.43
1.6
0.51
0.00
4.43
Total (1) + (2) + (3) + (4) 7.54 6.54
6-3-2 PC with Additional Units
Configuration: A C40K CPU, a C40P Expansion I/O Unit, an I/O Link Unit.
Program: 1150 addresses.
Average instruction execution time: 30 µs.
The equation for the cycle time from above is as follows:
Cycle time = Overseeing time
+ Input/output refreshing
+ Peripheral device servicing time
+ Instruction execution time
The overseeing time is fixed at 1.6 ms.
The input/output refresh time would be as follows: 0.51 ms + (0.03 ms x N ).
As the C40K is provided with only one input and one output word and the
C40P Expansion unit contains input and output words the value of the con-
stant N is 8. (i.e., N = 10 – 2 = 8) and so the time required is 0.51 ms + (0.03
ms x 8) = 0.75 ms.
The total execution time can be calculated by obtaining the average instruc-
tion execution time and multiplying this by the number of addresses used in
the program. As given above the average instruction execution time is 30 µs.
Total execution time = 1150 addresses x 30 µs = 34.50 ms
The peripheral device servicing time is calculated by adding the other three
time values and multiplying the result by a factor of 0.05. This value is only
required in configurations where a peripheral device is connected to the PC.
The result is calculated as an example. As there are no peripheral devices
used in this example the following results will be ignored in the final calcula-
tion.
Peripheral device servicing = (1.6 ms + 0.75 ms + 34.50 ms) x 0.05 =
1.84 ms which is rounded down to 1.50 ms.
Calculations
Calculating Cycle Time Section 6-3