486
6-5 I/O Response Time
The I/O response time is the time it takes for the PC to output a control signal
after it has received an input signal. The time it takes to respond depends on the
cycle time and when the CPU receives the input signal relative to the input re-
fresh period.
The minimum and maximum I/O response time calculations described below
are for where bit 000000 is the input bit that receives the signal and bit 000200 is
the output bit corresponding to the desired output point.
0000
00
00020
00
6-5-1 I/O Units Only
Here, we’ll compute the minimum and maximum I/O response times for a
CV1000 set for cyclic refreshing. The PC controls only I/O Units, mounted on the
CPU Rack, Expansion CPU Rack, or Expansion I/O Rack. The calculation is
identical for asynchronous and synchronous operation.
The data in the following table is used to produce the minimum and maximum
cycle times shown calculated below.
Input ON delay 1.5 ms
Cycle time 20 ms
Output ON delay 15 ms
The PC responds most quickly when it receives an input signal just prior to the
input refresh period in the cycle. Once the input bit corresponding to the signal
has been turned ON, the program will have to be executed once to turn ON the
output bit for the desired output signal and then the output refresh operation re-
freshes the output bit. The I/O response time in this case is thus found by adding
the input ON delay time, the cycle time, and the output ON delay time. This situa-
tion is illustrated below.
Cycle time
Input
signal
Output
signal
Cycle
Cycle time
I/O refresh
Overseeing
I/O response time
CPU reads
input signal
Output ON delay
Input ON delay
CPU writes
output signal
Program execution Program execution
Minimum I/O response time = input ON delay + cycle time + output ON delay
Minimum I/O response time = 1.5 + 20 +15 = 36.5 ms
Minimum I/O Response
Time
I/O Response Time Section 6-5
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