Specifications

Bulletin No. VVDED397044US R12/00 Section 1—Installation & Configuration
December 2000 Optimizing Network Performance
© 1998–2000 Schneider Electric All Rights Reserved
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Figure 25: Using the Command Semaphore
OPTIMIZING NETWORK PERFORMANCE
To optimize network performance consider the following points during
network design and implementation:
1. When structuring the information exchange requirements for a
network, consider the speed of the communication required to
implement the application properly.
— Use the communication method which best matches the speed
requirements of the information exchange.
— Communicate information only when the application requires it.
— Minimize network traffic by design. For example, when controlling
a simple process requiring only the control functions contained in
the first several command registers available via peer cop, set up
peer cop to send only those registers. This minimizes network
traffic and maintains best overall network speed.
2. For better network security, keep drive controllers and their
associated control devices on the same local network. As far as
possible, minimize or eliminate the need for drive controller signals to
cross network bridges.
3. Use command with no monitoring of communication faults (W402, Bit
14 set to 1) during troubleshooting and start-up operations.
Do not
Modicon PLC
Node 1
HMI
Node 2
Modicon
PLC Node 3
MODBUS PLUS Network 1
Node 4
Node 5
HMI sends MB Plus
commands to reserve
the command
semaphore in drive
controller 1.
Command
message to drive
controller 1
(Node 4) is
refused since
node 2 has
reserved the
command
semaphore of
drive controller 1.
Peer cop=Yes, with semaphore
(control) reserved by Node 2, causes
drive controller 1 (Node 4) to ignore
peer cop data and to take commands
only from Node 2. Other nodes
attempting to control drive controller 1
(Node 4) with a message are refused.
Drive controller 1 (Node 4) writes its
status using global data Xfer when
sending the token (other nodes may
monitor reservation of command
semaphore, including the command
node).
Drive 1 Drive 2
Peer cop node = Yes
Command node = 1
Drive controller writes its
status using global data
Xfer when sending the
token. Drive controller 2
(Node 5) allows
command parameters to
be written by any node
(including across
bridges), since command
semaphore is free and
peer cop = No.