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The PC takes longest to respond when it receives the input signal just after
the input 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
input refresh time would not need to be added in because the input comes
just after it rather than before it.
Input
signal
Output
signal
Cycle
Cycle time
I/O refresh
I/O response time
CPU reads
input signal
CPU writes
output signal
Output ON delay
Input ON delay
Overseeing
Cycle time
Maximum I/O response time = input ON delay + (cycle time x 2) + overseeing
time + 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
Cycle time 20 ms
Input refresh time 0.23 ms
Overseeing time 3.0 ms
Output ON-delay 15 ms
Minimum I/O response time = 1.5 + 20 + 0.23 + 3.0 +15 = 39.73 ms
Maximum I/O response time = 1.5 + (20 x 2) + 3.0 +15 = 59.5 ms
Maximum I/O Response
Time
Calculation Example
I/O Response Time Section 6-5