ABB ACS550-02 User Manual page 152

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Standard Serial Communication
This section describes ACS550 serial communication.
• The ACS550 includes, as standard, Modbus® communication on the RS485 port
(terminals 28...32).
• You can connect other fieldbus types using a special fieldbus adapter module
connection to option slot 2. For more information on fieldbus options, contact your
supplier.
When using serial communication, the ACS550 can either:
• Receive all of its control information from the fieldbus, or
• Be controlled from some combination of fieldbus control and other available
control locations, such as digital or analog inputs, and the control panel.
Introduction to Modbus
The Modbus protocol was introduced by Modicon, Inc. for use in control
environments featuring Modicon programmable controllers. Due to its ease of use
and implementation, this common PLC language was quickly adopted as a de-facto
standard for integration of a wide variety of master controllers and slave devices.
Modbus is a serial, asynchronous protocol. Transactions are half-duplex, featuring a
single Master controlling one or more Slaves. While RS232 can be used for point-to-
point communication between a single Master and a single Slave, a more common
implementation features a multi-drop RS485 network with a single Master controlling
multiple Slaves. The ACS550 features RS485 for its Modbus physical interface.
Modbus specification defines two distinct transmission modes: ASCII and RTU. The
ACS550 supports RTU only.
The remainder of this chapter assumes that you have a basic understanding of the
Modbus Protocol and its application in a control environment. If you need additional
information regarding Modbus, contact your ABB supplier for a copy of the Modbus
Protocol Reference Guide.
Activating Modbus Protocol
Per the default factory setting, fieldbus control is not operational. To activate
standard Modbus, set parameter 9802
single modification, the ACS550 is ready to communicate via the RS485 port using
the default communication settings. At this point, you can read and write drive
parameters using serial communication.
Start-Up
= 1 (
COMM PROT SEL STD MODBUS
). After this