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The PC takes longest to respond when it receives the input signal just after
the I/O refresh phase of the cycle. In this case the CPU does not recognize
the input signal until the end of the next cycle. The maximum response time
is thus one cycle longer than the minimum I/O response time, except that the
I/O refresh time would not need to be added in because the input comes just
after it rather than before it.
Cycle time
Input
signal
Output
signal
Cycle
Cycle time
I/O refresh
I/O response time
Input
ON delay
Instruction
execution
Instruction
execution
Instruction
execution
CPU reads
input signal
Output
ON delay
Cycle time
Maximum I/O response time = input ON delay + (cycle time x 2) + output ON
delay
The data in the following table would produce the minimum and maximum
cycle times shown calculated below.
Input ON-delay 1.5 ms
Output ON-delay 15 ms
Cycle time 20 ms
Minimum I/O response time = 1.5 + 20 + 15 = 36.5 ms
Maximum I/O response time = 1.5 + (20 x 2) +15 = 56.5 ms
Maximum I/O Response
Time
Calculation Example
I/O Response Time Section 6-4
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