Precautions On High Traffic In Fins Communications - Omron CJ1W-ETN21 - 04-2009 Operation Manual

Precautions on High Traffic in FINS Communications

CPU Bus Unit service cycle (local node 1)
CPU Bus Unit service processing time (local node 1) 0.4 ms
Transmission processing time (command)
Transmission delay (command)
Reception processing time (command)
CPU Bus Unit service cycle (remote node)
CPU Bus Unit service processing time (remote node) 0.6 ms
Transmission processing time (response)
Transmission delay (response)
Reception processing time (response)
CPU Bus Unit service cycle (local node 2)
CPU Bus Unit service processing time (local node 2) 0.4 ms
Total
6-7

Precautions on High Traffic in FINS Communications

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 receiving 256 words between
two PLC nodes using RECV(098). Calculations are shown in the following
table:
Conditions
Local node CPU cycle time:
Local node CPU processing mode:
Local node CPU uniform peripheral servicing time:
Remote node CPU cycle time:
Remote node CPU processing mode:
Remote node CPU uniform peripheral servicing time: Default (4%)
Baud rate:
Item
When applications are constructed using FINS communications services,
communications errors (from multiple response timeouts) may occasionally
occur due to high traffic, depending on the system configuration and the appli-
cation programs. This section describes precautions for systems with high
traffic in FINS communications.
■
Conditions for High Traffic
High traffic may occur if FINS messages from multiple communicating nodes
are concentrated at a single Ethernet Unit. The Ethernet Unit and the CPU
Unit may have insufficient processing capacity for the volume of FINS mes-
sages (commands) that are coming from the network.
10 ms
Normal
Default (4%)
15 ms
Normal
100Base-TX
Calculations
10 ms
0.550 ms ≈ 0.5 ms
0.0118 ms ≈ 0.1 ms
0.704 ms ≈ 0.7 ms
15 ms
256 × 0.002 + 0.550 = 1.062 ≈ 1.1 ms
256 × 0.0013 + 0.0118 = 0.3446 ≈ 0.3 ms
256 × 0.003 + 0.704 = 1.472 ≈ 1.5 ms
10 ms
10 + 0.4 + 0.5 + 0.1 + 0.7 + 15 + 0.6 + 1.1 + 0.3
+ 1.5 + 10 + 0.4 = 40.6 ms
Section 6-7
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