207
Data Link I/O Response Time
Section 8-3
2.
Data exchange occurs just after the PC at node #1 passes the token that
makes it the polling node, causing a delay of up to one communications cy-
cle time before the data is transferred in data link processing.
3.
At node #7, data from the previous data exchange is still being transferred,
causing a delay of up to one cycle before the input is read into the PC.
4.
The data transferred in data link processing arrives at the PC at node #7
after data exchange, so the data will not be read into the PC until the next
data exchange, causing a delay of up to one peripheral servicing interval.
Up to 3,700 words can be transferred in a single data exchange, so a delay
of another peripheral servicing interval will occur if more than 3,700 words
are being transferred.
5.
The data is received after the PC at node #7 has executed the instruction,
causing a delay of up to one cycle time.
Assume that the peripheral servicing interval of the PCs at nodes #1 and #7 is
10 ms. The equation for maximum data link I/O response time is as follows:
Note If the total number of data link words is greater than the maximum number of
words that can be exchanged per data exchange, the maximum data link I/O
response time will be cycle time of PC at node #7
×
3.
Noise may increase I/O delays.
Minimum Response Time
Input ON delay
1.5 ms
Cycle time of PC at node #1
×
2
15 ms
×
2
Peripheral servicing interval of PC at
node #1
10 ms
Communications cycle time
×
4
9.9 ms
×
3
Peripheral servicing interval of PC at
node #7
×
2
10 ms
×
2
PC cycle time at node #7
×
2 (see note)
20 ms
×
2 (see note)
Output ON delay
15 ms
Total (data link I/O response time)
146.2 ms
Input
Input device
Input ON delay
1 cycle
I/O refresh
PC at node #1
PC at node #7
Peripheral servicing interval
Peripheral servicing interval
Output device
Output
ON delay
Data link I/O response time
Program
◆
◆
Program
Data link transmission
Data processing time
Data processing time
Summary of Contents for CVM1-CLK21
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