Omron CS1W-ETN21 CPU Bus Unit Service Processing Time Remote Node, Example Calculations

Communicating between OMRON PLCs Section 6-6

CPU Bus Unit Service Processing Time (Remote Node)

The processing time will be as follows, depending on the CPU processing mode settings at the CPU Unit.

CPU processing mode	Processing time considerations
settings
Normal Mode	Set peripheral servicing time
	Default: 4% of CPU Unit cycle time
Priority peripheral servicing	Ethernet Unit is given	Time slice peripheral servicing
	priority.	execution time
	Ethernet Unit is not	Set peripheral servicing time
	given priority.	(Default: 4% of CPU Unit cycle
		time)
Parallel processing with syn-	Set peripheral servicing time
chronous memory access	(Default: 4% of CPU Unit cycle time)
Parallel processing with	1 ms max.
asynchronous memory
access

For details, refer to the CPU Unit operation manual.

Note The actual operating environment can cause transmission delays larger than those calculated with the methods given here. Among the causes of longer delays are the following: traffic on the network, window sizes at network nodes, traffic through the Ethernet Unit (e.g., socket servicing, FTP server communications, etc.), and the system configuration.

Example Calculations

The following example shows calculations for sending 256 words between two

PLC nodes using SEND(090). Calculations are shown in the following table.

Conditions

Local node CPU cycle time: 10 ms

Local node CPU execution mode: Normal

Local node CPU uniform peripheral servicing time: Default (4%)

Remote node CPU cycle time: 5 ms

Remote node CPU execution mode: Normal

Remote node CPU peripheral servicing time: Default (4%)

Baud rate: 100Base-TX

Item		Calculation
CPU Bus Unit service cycle (local node)	10 ms
CPU Bus Unit service processing time	0.4 ms
(local node)
Transmission processing time	256 ⋅	0.002 + 0.550 = 1.062 ≈	1.1 ms
Transmission delay	256 ⋅	0.0013 + 0.0118 = 0.3446 ≈
	0.3 ms
Reception processing time	256 ⋅	0.003 + 0.704 = 1.472 ≈	1.5 ms
CPU Bus Unit service cycle (remote node)	5 ms
CPU Bus Unit service processing time	0.2 ms
(remote node)
Total	10 + 0.4 + 1.1 + 0.3 + 1.5 + 5 + 0.2 =
	18.5 ms

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