4-11-2 Data Exchange Timing - Omron CS1W-SLK11-21 - 06-2004 Manual

Data Link Characteristics
Example Calculations
Note

4-11-2 Data Exchange Timing

PLC processing
Basic processing
64
result indicates the communications cycle time has been decreased and a
negative result indicates it has been increased. Round the result of the calcu-
lation to the nearest millisecond.
Change of the communications cycle time (coaxial cable systems) =
(old maximum node address - new maximum) × 0.085 ms
+ (old maximum number of frames - new maximum) × 0.654 ms
+ (old number of polled units - new number) × 0.750 ms
Change of the communications cycle time (optical fiber cable systems) =
(old maximum node address - new maximum) × 0.1115 ms
+ (old maximum number of frames - new maximum) × 0.77 ms
+ (old number of polled units - new number) × 0.75 ms
The examples below calculate the change of the communications cycle time
for both coaxial and optical fiber cable when the other network parameters are
changed as shown below:
Maximum node address: . . . . . .Changed from 62 to 16
Maximum number of frames: . . .Changed from 10 to 13
Number of polled units: . . . . . . .Changed from 4 to 5
Change of the communications cycle time (coaxial cable systems) =
(62 – 16) × 0.085 ms + (10 – 13) × 0.654 ms + (4 – 5) × 0.75 ms =
1.198 ms (1 ms after rounding)
Change of the communications cycle time (optical fiber cable systems) =
(62 – 16) × 0.1115 ms + (10 – 13) × 0.77 ms + (4 – 5) × 0.75 ms =
2.069 ms (2 ms after rounding)
(1) If the maximum node address is set to a value less than the node address
of any nodes in the data link, those nodes will no longer be part of the
data links.
(2) If the maximum number of frames is set too low, errors might occur during
the execution of operations such as SEND(90), RECV(98), and
CMND(490) instructions, internode echo tests, and remote monitoring.
(3) Lowering the number of polled units will increase the delay between re-
setting a Unit or turning on its PLC's power and its entrance into the net-
work.
This section explains data link timing when using data links between SYS-
MAC LINK Units and a CPU Unit.
With a CS-series PLC, data exchange with the SYSMAC LINK Unit is per-
formed by interrupt processing during the peripheral servicing time in the CPU
Unit cycle time. Data exchange timing is as follows:
PLC cycle time
CPU Bus
Execution
Unit service
Interrupt processing
I/O refreshing
for data exchange
If interrupt processing for data exchange is executed, the PLC cycle time will
be lengthened by the time required for the interrupt processing.
Programming
Device/Host Link Execution
service
Basic processing
Section 4-11