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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.
For details, refer to the CPU Unit operation manual.
Transmission Processing
(Response)
Number of words sent
× 0.003 + 0.704 ms
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
CPU execution mode Processing time considerations
Normal Mode 4% of CPU Unit cycle time
Priority peripheral ser-
vicing
Ethernet Unit is given
priority.
Time slice peripheral servicing
execution time
Ethernet Unit is not
given priority.
Set peripheral servicing time
(Default: 4% of CPU Unit cycle
time)
Parallel processing with
synchronous memory
access
Set peripheral servicing time
(Default: 4% of CPU Unit cycle time)
Parallel processing with
asynchronous memory
access
1 ms max.
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
node) (command)
256 × 0.003 + 0.704 = 1.472 ≈ 1.5 ms
CPU Bus Unit service cycle (local
node)
10 ms
CPU Bus Unit service processing
time (local node)
0.4 ms
Transmission processing time (local
node) (response)
0.704 ms ≈ 0.7 ms
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