48
The equation for maximum I/O response time is as follows:
Response time = input ON delay + (scan time of PC of Unit 0 x 3) + (PC Link
polling time x 2 + induction sequence processing time) +
(scan time of PC of Unit 7 x 2) + output ON delay
Inserting the same values plus the following values into this equation pro-
duces a maximum I/O response time of 236.5 ms.
PC Link polling time: 30 ms
Induction sequence processing time: 0 ms
C1000H and C2000H PCs
Although the scan for C1000H and C2000H PCs is slightly different from that
for the C500 PC, the data flow that produces the minimum response time
between input and output and the equation for computing it are the same as
those shown for C500 PCs. Using the minimum transmission time of 12.5 ms
in the equation produces a minimum I/O response time of 99 ms.
The following diagram illustrates the data flow that will produce the maximum
response time for a Single-level PC Link System. Delays occur because sig-
nals or data is received just after they would be processed or because data is
sent during processing. In either case, processing must wait until the next
scan/polling cycle.
The polling delay is the result of the LR data in its PC being updated immedi-
ately after the previous was sent to the buffer in the PC Link Unit, cause a
delay until the next polling cycle. One more polling cycle is then required be-
fore the data reaches the buffer in PC Link Unit 7.
Program
executed.
PC with
Unit 0
Buffer in
Unit 0
PC Link
Unit trans-
missions
Buffer in
Unit 7
Input
Output
Polling
delay
Scan time
Scan time Output refresh
PC Link Unit
servicing
PC Link
polling time
Induction sequence
processing time
Maximum
transmission
time
PC Link Unit servicing
PC with
Unit 7
Output refresh
Input re-
freshed
Program
executed.
The equation for maximum I/O response time is thus as follows:
Response time = input ON delay + (scan time of PC of Unit 0 x 2) + (PC Link
polling time x 2 + induction sequence processing time) +
(scan time of PC of Unit 7 x 2) + output ON delay
Inserting the same values plus the following values into this equation and
again using the minimum transmission time produces a maximum I/O re-
sponse time of 336.5 ms.
Minimum Response Time
Maximum Response Time
Response Times Section 6-1