8-3
Section
Data Link I/O Response Time
122
8-3-2 PC to Computer
In the following diagram illustrating the maximum data link I/O response time, a
CS1-series PC is used for the PC (#2) and the PC’s cycle time is greater than or
equal to the communications cycle time.
User application
PC at node #2
(ClkReadDatalink)
Late
1 cycle
Program
Communications
cycle time
1
2
3
Input device
Data link I/O response time
Input
I/O refresh
Data exchange
(*)
Data link
transmissions
Late
Computer at node #1
Input ON response time
Receive processing
(FinsGateway)
There are three points shown in the diagram above where processing is
delayed, increasing the data link I/O response time.
1, 2, 3...
1. The input arrives in the PC just after I/O refreshing, causing a delay of up to
one cycle before the input is read into the PC.
2. Data exchange occurs just after the PC at node #2 passes the token that
makes it the polling node, causing a delay of up to one communications
cycle time before the data is transferred in data link processing.
3. The data arrives at the Data Link Area of the Support Board mounted at the
computer at node #1, but processing is delayed until the user application
executes the ClkReadDatalink library function. This delay will vary depend-
ing on the contents of the user application.
Note
1. Noise may increase I/O delays.
2. The data send processing time for the area marked by the asterisk (*) in the
diagram will be affected by the processing capacity of the computer that is
used.
3. The communications cycle time may fluctuate.
4. Refer to the Controller Link Units Operation Manual (W309) for details on
the time required for data exchanges between the Controller Link Unit and
the PC.
