RLE LD5100 - Manual (Page 49)

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C
H A P T E R
C HAPTER 0
M
ODBUS
C
OMMUNICATION
This document describes the Modbus communications protocol as supported by the LD5100
Water Leak Detection System. It includes details and information on how to configure the
LD5100 for communications via Modbus network.
8.1. Implementation Basics
The LD5100 is capable of communicating via the half-duplex RS485 serial communication
standard. The LD5100 is configured to act as a slave device on a common network. The
RS485 medium allows for multiple devices on a multi-drop network. The LD5100 is a slave
only device and will never initiate a communications sequence.
8.1.1 Modes of Transmission
The Modbus protocol uses ASCII and RTU modes of transmission. The LD5100 supports only
the RTU mode of transmission, with 8 data bits, no parity and one stop bit. Every Modbus
packet consists of four fields:
 Slave Address Field
 Function Field
 Data Field
 Error Check Field (Checksum)
8.1.1.1 Slave Address Field
The slave address field is set by the going into local 160x160 display on the front panel. Go to
COMM PORT SETTINGS from the Main Menu screen. Select the Modbus Slave address and
the baud rate to be used for either/or EIA-485 Port1 and EIA-485 Port2.