Maximum Transmission Delays: Writing/Reading to CPU Unit

Section 7-5

For details, refer to the CPU Unit operation manual.

CPU Bus Unit Service Processing Time

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

CPU execution mode

Processing time considerations

 

 

Normal Mode

4% of CPU Unit cycle time

 

 

 

Priority peripheral ser-

Ethernet Unit is given

Time slice peripheral servicing

vicing

priority.

execution time

 

 

 

 

Ethernet Unit is not

Set peripheral servicing time

 

given priority.

(Default: 4% of CPU Unit cycle

 

 

time)

 

 

 

Parallel processing with

Set peripheral servicing time

synchronous memory

(Default: 4% of CPU Unit cycle time)

access

 

 

 

 

 

Parallel processing with

1 ms max.

 

asynchronous memory

 

 

access

 

 

 

 

 

For details, refer to the CPU Unit operation manual.

Transmission Processing Number of words sent 0.003 + 0.704 ms

(Response)

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., simultaneous socket servicing and 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

CPU cycle time: 10 ms

CPU execution mode: Normal

CPU uniform peripheral servicing time: Default (4%)

Baud rate: 100Base-TX

Item

Calculation

 

 

Personal computer transmission pro-

---

cessing time

 

 

 

Transmission delay (command)

256 0.0013 + 0.0118 = 0.3446 0.3 ms

 

 

Reception processing time local

256 0.003 + 0.704 = 1.472 1.5 ms

node) (command)

 

 

 

CPU Bus Unit service cycle (local

10 ms

node)

 

 

 

CPU Bus Unit service processing

0.4 ms

time (local node)

 

 

 

Transmission processing time (local

0.704 ms 0.7 ms

node) (response)

 

 

 

Transmission delay (command)

0.0118 ms 0.1 ms

 

 

Personal computer reception pro-

---

cessing time

 

 

 

Maximum transmission delay time

Personal computer transmission/reception

 

processing time + 0.3 +1.5 + 10 + 0.4 + 0.7 +

 

0.1 = personal computer transmission/recep-

 

tion processing time + 13.0 ms

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Omron CJ1W-ETN21 operation manual 194