Usb Interface; Data Frame Format And Data Rate; Data Packet Format - GE 350 Communications Manual

GE
Digital Energy
SR350 Feeder Protection System
Chapter 6: USB interface
MODBUS Protocol

Data Frame Format and Data Rate

Data Packet Format

350 FEEDER PROTECTION SYSTEM – COMMUNICATIONS GUIDE

USB interface

The USB inferface supports only the Modbus protocol.
For information on using the USB port on the 350 relay, please refer to section 3 of the
350 Instruction Manual.
The 350 implements a subset of the Modicon Modbus RTU serial communication standard.
The Modbus protocol is hardware-independent. That is, the physical layer can be any of a
variety of standard hardware configurations. This includes USB, RS485, fibre optics, etc.
Modbus is a single master / multiple slave type of protocol suitable for a multi-drop
configuration.
The 350 is always a Modbus slave. It can not be programmed as a Modbus master.
Computers or PLCs are commonly programmed as masters.
Both monitoring and control are possible using read and write register commands. Other
commands are supported to provide additional functions.
The Modbus protocol has the following characteristics.
• Address: 1 to 254
• Supported Modbus function codes: 3H, 4H, 5H, 6H, 7H, 8H, 10H
One data frame of an asynchronous transmission to or from a 350 typically consists of 1
start bit, 8 data bits, and 1 stop bit. This produces a 10 bit data frame. This is important for
transmission through modems at high bit rates.
Modbus protocol can be implemented at any standard communication speed. The
350 supports operation at 9600, 19200, 38400, 57600, and 115200 baud. The USB
interface will support only 115200 baud.
A complete request/response sequence consists of the following bytes (transmitted as
separate data frames):
6–1