Rs485 Modbus Rtu Serial Communications; Transmission Specification; Connection; Serial Interface Configuration - GE AF-300 P11 User Manual

12. RS485 Modbus RTU Serial Communications

The serial interface supports operation, configuration and monitoring of drive functions through an EIA/RS485 connec-
tion. The serial interface is based on Modbus RTU protocol. This protocol allows the drive to function as an RTU slave
on an industrial network.

12.1 Transmission Specification

Item
Physical level
Transmission distance
Number of nodes
Transmission speed
Transmission mode
Transmission protocol
Character code
Character length
Error check

12.2 Connection

Connection method
Use shielded wire and connect to the control terminals (DX-, DX+ and SD). A termination resistor should be added
between the data lines on the each end of the network. The value of the termination resistor depends on the character-
istic impedance of the cable. A common value for termination resistors is 120 ohms.
Control terminals
Terminal
marking
DX+
DX-
SD

12.3 Serial Interface Configuration

Drive function codes H30 to H39 are used to configure the serial interface parameters, such as device address, baud
rate and error response.

12.4 Modbus RTU Functions

The following RTU functions are supported. The maximum number of consecutive parameters for function 03 and 16
messages is 16.
Code Description
03 Read Holding Registers (16 registers maximum)
06 Preset Single Register
16 Preset Multiple Registers (16 registers maximum)
Data subject to change without notice 7/07. © 2007 GE Drives
Specification
EIA/RS485
500 m max.
32 total
19200, 9600, 4800, 2400 [bits/s]
Half duplex
Modbus RTU
Binary
8 bits
CRC
Terminal name
RS485 communication data (+)
RS485 communication data (–)
Cable shield
Function description
Input/output terminals for RS485
communication.
Electrically floating
12-1