8-2
Section
CPM2A/CPM2C Cycle Time and I/O Response Time
524
Cycle Time Example
In this example, the cycle time is calculated for a CPM2A/CPM2C CPU Unit with
30 I/O points (18 input points and 12 output points). The I/O is configured as fol-
lows:
18 inputs:
2 words (00000 to 00011, 00100 to 00105)
12 outputs: 2 words (01000 to 01007, 01100 to 01103)
The rest of the operating conditions are assumed to be as follows:
User’s program:500 instructions (consists of only LD and OUT)
Cycle time:
Variable (no minimum set)
The average processing time for a single instruction in the user’s program is as-
sumed to be 1.26
µ
s. The cycle times are as shown in the following table.
Process
Calculation method
Time with
Programming Device
Time without
Programming Device
1. Overseeing
Fixed
0.3 ms
0.3 ms
2. Program execution
1.26
×
500 (
µ
s)
0.6 ms
0.6 ms
3. Cycle time calculation
Negligible
0 ms
0 ms
4. I/O refreshing
Fixed
0.3 ms (CPM2C: 0.06 ms)
0.3 ms (CPM2C: 0.06 ms)
5. Peripheral port servicing
Minimum time
0.55 ms
0 ms
Cycle time
(1) + (2) + (3) + (4) + (5)
1.75 ms (CPM2C: 1.51 ms)
1.2 ms (CPM2C: 0.96 ms)
Note
1. The cycle time can be read from the PC via a Programming Device.
2. The maximum and current cycle time are stored in AR 14 and AR 15.
3. The cycle time can vary with actual operating conditions and will not neces-
sarily agree precisely with the calculated value.
8-2-2 I/O Response Time
The I/O response time is the time it takes after an input signal has been received
(i.e., after an input bit has turned ON) for the PC to check and process the in-
formation and to output a control signal (i.e., to output the result of the proces-
sing to an output bit). The I/O response time varies according to the timing and
processing conditions.
The minimum and maximum I/O response times are shown here, using the fol-
lowing program as an example.
Input
Output
The following conditions are taken as examples for calculating the I/O response
times.
Input ON delay:
10 ms (input time constant: default setting)
Overseeing time:
1 ms (includes I/O refreshing)
Instruction execution time:
14 ms
Output ON delay:
15 ms
Communications ports:
Not used.
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