Omron SYSMAC LINK C1000H-SLK21-V1 System Manual page 84

Data Link Characteristics
Case 3
Input
Input device
Input ON delay
X
(1)
Program
1, 2, 3...
70
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 y the commu-
nications cycle time.
1 cycle
X
(2)
A
Communications
cycle time
Previous communica-
tions cycle data
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 exchange is still being transferred, so new
data cannot be exchanged, causing a delay of one communications cycle
time. Furthermore, the data exchange then occurs just after the PC at node
#1 passes the token for the polling unit, causing another delay of one com-
munications 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 (15 ms) × 2
+ communications cycle time (19 ms) × 3 + PC cycle time at node #7 (50 ms) × 3*
+ output ON delay (15 ms) = 253.5 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 303.5 ms.
2. Noise may increase I/O delays.
PC at node #1
SYSMAC LINK Unit
transmission processing
Data link transmission
X
(3)
SYSMAC LINK Unit
transmission processing
X
(4)
1 cycle
Output device
Section 5-10
I/O refresh
Data exchange
Program
Output ON delay
Output