Rs485 Installation And Set-Up; Installation And Set-Up; Network Connection; Mg35M402 - GE AF-650 GP Design And Installation Manual

RS485 Installation and Set-...

9 RS485 Installation and Set-up

9.1 Installation and Set-up

9.1.1 Network Connection

One or more frequency converters can be connected to a
control (or master) using the RS485 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 1 frequency converter is connected to a
master, use parallel connections.
9 9
Illustration 9.1 Parallel Connections
To avoid potential equalizing currents in the shield, wire
according to Illustration 2.5.

9.1.2 RS485 Bus Termination

Terminate the RS485 bus by a resistor network at both
ends. For this purpose, set switch S801 on the control card
for "ON".

9.1.3 EMC Precautions

The following EMC precautions are recommended to
achieve interference-free operation of the RS485 network.
Observe relevant national and local regulations, for
example, regarding protective ground connection. Keep
the RS485 communication cable 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 sufficient, but keeping the greatest
possible distance between the cables is recommended,
especially where cables run in parallel over long distances.
When crossing is unavoidable, the RS485 cable must cross
motor and brake resistor cables at an angle of 90°.
88

9.2 Network Configuration

To enable Modbus RTU on the frequency converter, set the
parameters in Table 9.1.
Parameter
Parameter O-30 Protocol
Parameter O-31 Address
Parameter O-32 Drive Port
Baud Rate
Parameter O-33 Drive Port
Parity
Table 9.1 Modbus RTU Parameters
9.2.1 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 2 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 Formats

9.2.2 Modbus RTU Message Structure

The transmitting device places a Modbus RTU message
into a frame with a known beginning and ending point.
This allows receiving devices to begin at the start of the
message, read the address portion, determine which
device is addressed (or all devices, if the message is
broadcast), and to recognize when the message is
completed. Partial messages are detected and errors set as
a result. Characters for transmission must be in
hexadecimal 00 to FF format in each field. The frequency
converter continuously monitors the network bus, also

DET-767c All rights reserved.

Setting
Modbus RTU
1–247
2400–115200
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
Cyclic Redundancy Check (CRC)
Stop

MG35M402