Omron SYSMAC LINK C1000H-SLK21-V1 System Manual page 85

Data Link Characteristics
Case 4
Input
Input ON delay
X
(1)
1, 2, 3...
The following diagram illustrates the data flow that will produce the maximum
data link I/O response time when the cycle time of the PC at node #1 t the com-
munications cycle time and the cycle time of the PC at node #7 t the commu-
nications cycle time.
Input device
1 cycle
Program
X
(2)
A
Communications
cycle time
PC at node #7
Data link I/O response time
There are three points shown in the diagram above where processing is
delayed, increasing the data link I/O response time.
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. At point A data from the previous data exchange is still being transferred, so
the new data cannot be exchanged, causing a delay of up to one commu-
nications cycle time. Furthermore, the data exchange then occurs just after
the PC at node #1 passes the token that makes it the polling unit, causing
another delay of up to one communications cycle time before the data is
transferred in data link processing.
3. The data transferred in data link processing arrives at the PC at node #7
while data exchange is taking place, so the data will not be read into the PC
until the next data exchange, causing a delay of up to one cycle.
Up to 1,642 words can be transferred in a single data exchange, so a delay
of another cycle will occur if more than 1,642 words are being transferred.
The equation for maximum data link I/O response time is as follows:
Response time =
input ON delay (1.5 ms) + cycle time of PC at node #1 (15 ms) × 2
+ communications cycle time (19 ms) × 3 + PC cycle time at node #7 (15 ms) × 2*
+ output ON delay (15 ms) = 133.5 ms*
Note 1. *If more than 1,642 words are being transferred, 3 cycles of the PC at node
#7 are required and the total response time becomes 148.5 ms.
2. Noise may increase I/O delays.
PC at node #1
SYSMAC LINK Unit
transmission processing
Data link transmission
SYSMAC LINK Unit
transmission processing
(3)
X
Program
1 cycle
Output device
Section 5-10
I/O refresh
Data exchange
Output ON
delay
Output
71