334
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
Calculation Example The
data in the following table would produce the minimum and maximum cycle
times shown calculated below.
Item Time
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
Note In this example the I/O refresh time is negligible has not been included in the
minimum I/O response time.
6-4-2 Remote I/O Systems
With C200HS Remote I/O Systems, only the cycle
time of the PC needs to be
considered
in computing the I/O response times as long
as the remote I/O trans
-
mission
time is negligible and smaller than the cycle time. The cycle time, how
-
ever, is increased by the presence of the Remote I/O System.
The
processing that determines and the methods for calculating maximum and
minimum
response times from input to output are
provided in this section. Calcu
-
lations assume that both the input and the output are located on Slave Racks in a
Remote
I/O System, but the calculations are the same for I/O points on Optical
I/O Units, I/O Link Units, I/O Terminals, etc.
X
Input
on
Slave Rack
Output on
Slave Rack
Although
more precise
equations are possible if required, equations used for the
following calculations do not consider fractions of a scan.
Maximum I/O Response
Time
I/O Response Time Section 6-4
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