RLE LD2000 - Manual (Page 51)

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C
H A P T E R
C HAPTER 4
M
ODBUS
C
OMMUNICATION
This chapter describes the Modbus communication protocol as supported by the LD2000
Distance Read System. The content includes details and information on how to configure the
LD2000 for communications via Modbus network
5.1. Implementation Basics
The LD2000 is capable of communicating via the half-duplex EIA-485 serial communication
standard. The LD2000 is configured to act as a slave device on a common network. The EIA-
485 medium allows for multiple devices on a multi-drop network. The LD2000 is a slave only
device and will never initiate a communications sequence.
5.1.1 Modes of Transmission
The Modbus protocol uses ASCII and RTU modes of transmission. The LD2000 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)
5.1.1.1 Slave Address Field
The slave address field is one byte in length and identifies the slave device involved in the
transaction. A valid address range is between 1 and 254. The slave address is set from the
Modbus/EIA-485 Configuration webpage (see 4.3.9, “Modbus” on page 43).