112
3-10-1
Single PCs
Both input and output refreshes are performed at the same time in the CPU
cycle, after the program process has been completed. The following section
show how the maximum and minimum I/O response times may be calcu-
lated.
The PC responds most quickly when it receives an input signal just prior to
the I/O refresh period in the scan. 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. The I/O response time in
this case is thus found by adding the input delay, the scan time, and the out-
put delay. This situation is illustrated below.
Input delay
IN
OUT
PC Process
Execution
Execution
Execution
Scan time
Output delay
T
min
A
B
C D
E
A
B
C D E
B
D
E
C
T
min
= Minimum I/O response time
= input delay + filter time + scan time + output delay
= C + B + (300
µ
s + program execution time) + A
where A:
Output delay (see table below)
B:
Filter value (refer to Section 2 Installation)
C:
Input delay (see table below)
and
Program execution time = sum of instruction execution times (refer to
Appendix C Programming Instructions and Execution Times)
The ON input delay is 300
µ
s maximum and the OFF input delay is 250
µ
s
maximum. Output delays are given in the following table.
Output
Relay
Transistor
ON output delay
10 ms max.
20
µ
s max.
OFF output delay
10 ms max.
300
µ
s typical
The PC takes longest to respond when it receives the input signal just after
the I/O refresh phase of the scan. In this case the CPU does not recognize
the input signal until the end of the next scan. The maximum response time
is thus one scan longer than the minimum I/O response time.
Minimum I/O Response
Time
Maximum I/O Response
Time
I/O Response Time
Section 3-10