Installation And Setup; Bus Termination; Emc Precautions; Network Configuration - GE AF-650 GP Design And Installation Manual

RS-485 Installation and Set...
9 RS-485 Installation and Setup

9.1 Installation and Setup

9.1.1 Network Connection
One or more adjustable frequency drives can be connected
to a control (or master) using the RS-485 standardized
interface. Terminal 68 is connected to the P signal (TX+, RX
+), while terminal 69 is connected to the N signal (TX-,RX-).
If more than one adjustable frequency drive is connected
to a master, use parallel connections.
Figure 9.1
In order to avoid potential equalizing currents in the
screen, ground the cable screen via terminal 61, which is
connected to the frame via an RC-link.
9.1.2 RS-485 Bus Termination
The RS-485 bus must be terminated by a resistor network
at both ends. For this purpose, set switch S801 on the
control card to "ON".

9.1.3 EMC Precautions

The following EMC precautions are recommended in order
to achieve interference-free operation of the RS-485
network.
Relevant national and local regulations, for example
regarding protective ground connection, must be
observed. The RS-485 communication cable must be kept
away from motor and brake resistor cables to avoid
coupling of high frequency noise from one cable to
another. Normally a distance of 200 mm (8 inches) is
TM
AF-650 GP Design and Installation Guide
sufficient, but keeping the greatest possible distance
between the cables is generally recommended, especially
where cables run in parallel over long distances. When
crossing is unavoidable, the RS-485 cable must cross motor
and brake resistor cables at an angle of 90°.

9.2 Network Configuration

9.2.1 Adjustable Frequency Drive with
Modbus RTU
To enable Modbus RTU on the adjustable frequency drive,
set the following parameters
Parameter
O-30 Protocol
O-31 Address
O-32 Drive Port Baud Rate
O-33 Drive Port Parity
Table 9.1
9.2.2 Modbus RTU Message Framing
Structure
The controllers are set up to communicate on the Modbus
network using RTU (Remote Terminal Unit) mode, with
each byte in a message containing two 4-bit hexadecimal
characters. The format for each byte is shown in Table 9.2.
Start
bit
Table 9.2 Format for Each Byte
Coding System
Bits Per Byte
Error Check Field
Table 9.3
DET-767A
Setting
Modbus RTU
1–247
2,400–115,200
Even parity, 1 stop bit (default)
Data byte Stop/
parity
8-bit binary, hexadecimal 0-9, A-F. 2
hexadecimal characters contained in each 8-
bit field of the message
1 start bit
8 data bits, least significant bit sent first
1 bit for even/odd parity; no bit for no
parity
1 stop bit if parity is used; 2 bits if no parity
Cyclical Redundancy Check (CRC)
9 9
Stop
9-1