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6-1 Response Times
The processing that determines and the methods for calculating maximum
and minimum response times from input to output are provided in this sub-
section. The following System and I/O program steps will be used in all ex-
amples below. This System contains eight PC Link Units.
Although more precise equations are possible if required, equations used for
the following calculations do not consider fractions of a scan.
In looking at the following timing charts, it is important to remember the se-
quence processing occurs during the PC scan, particular that inputs will not
produce programmed-actions until the program has been execution.
X
PC Link Unit
PC
PC Link Unit
PC
X
X
Unit 0 Unit 7
Input on PC
of Unit 0
LR bit
Input LR XXXX
Output on PC
of Unit 7
LR XXXX
Input
Output
Output
Noise may increase I/O delays.
C500 PCs
The following illustrates the data flow that will produce the minimum re-
sponse time, i.e., the time that results when all signals and data transmis-
sions are processed as soon as they occur.
PC with
Unit 0
Buffer in Unit 0
PC Link Unit
transmissions
Buffer in Unit 7
Input
Output
Minimum transmission time
Program executed.
Scan time
Scan time
I/O refresh
PC Link Unit servicing
Program executed.
PC with
Unit 7
Note
Minimum Response Time
Response Times Section 6-1