Omron SYSMAC LINK C1000H-SLK21-V1 System Manual page 82

Data Link Characteristics
Maximum Response Time
Case 1
Input
Input device
Input ON delay
X
(1)
Program
1, 2, 3...
68
The maximum data link I/O response time is calculated for four cases.
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 nodes #1 and 7 are
greater than the communications cycle time.
1 cycle
X
(2)
SYSMAC LINK Unit
transmission processing
Communications
cycle time
PC at node #7
Data link I/O response time
There are four 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. Data exchange occurs just after the PC at node #1 passes the token that
makes it the polling unit, causing a delay of up to one communications cycle
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 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 (20 ms) × 2
+ communications cycle time (19 ms) × 3 + PC cycle time at node #7 (50 ms) × 3*
+ output ON delay (15 ms) = 263.5 ms*
Note 1. *If more than 1,642 words are being transferred, 4 cycles of the PC at node
#7 are required and the total response time becomes 313.5 ms.
2. Noise may increase I/O delays.
PC at node #1
Data link transmission
X X
(3)
Previous communica-
tions cycle data
1 cycle
Section 5-10
I/O refresh
Data exchange
SYSMAC LINK Unit
transmission processing
X
(4)
Program
Output device
Output ON delay
Output