RLE 10K V.2.5.a - Manual (Page 29)

rletech.com SeaHawk 10K User Guide 29
C
H A P T E R
C HAPTER 3
M
ODBUS
C
OMMUNICATION
4.1. Modbus Implementation Basics
The SeaHawk 10K uses its EIA-485 port to communicate via Modbus. The SeaHawk 10K is
configured to act as a slave device on a common network and is a slave only device – it will
never initiate a communications sequence.
4.1.1 Modes of Transmission
The SeaHawk 10K supports the Modbus 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)
4.1.1.1 Slave Address Field
The slave address field is one byte in length and identifies the slave device involved in the
transaction. The valid Modbus slave address range is between 1 and 254. The Modbus address
was set in Chapter 2, “TB3 and TB4: Input Power and EIA-485 Communications Port” on
page 17 . Refer to Figure 2.13, “SW2 DIP Switch Settings for Communications Address” on
page 19 for more specific information.
4.1.1.2 Function Field
The function field is one byte in length and tells the SeaHawk 10K which function to perform.
Functions are 03 (Read 4xxxx output registers) and 04 (Read 3xxxx input registers) are
supported by the SeaHawk 10K.