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ChaPTer 4: moDBuS
Modbus Zone setup
The Sentinel Pro can be configured to read from almost any modbus slave device and data format
through the correct selection of the settings described below. Attention to detail is vital when setting up
a modbus zone. If any of the below settings are not correct, the Sentinel Pro will fail to retrieve the data
from the slave device or will read incorrect values. If you are unsure of the correct setting, refer to the
user’s manual for the device you are trying to connect to. The various zone configuration settings are
explained in detail below.
Interface Type: Select the appropriate physical interface for your external
device. Choose between:
TCP: Modbus Communication over Ethernet port on the Sentinel Pro.
The slave devices from which data is to be read be able to communicate
to the Sentinel Pro over the LAN connection.
RS-485: Modbus Communicate over RS-485 using the terminal block
located on the Sentinel Pro.
Slave ID
: Unique number which identifies the Modbus slave device on the
network. All slave devices on an RS-485 network must have a unique
address (1-255). If necessary, refer to the manual of your modbus slave
device to determine how to changes the slave ID, also referred to as the
slave address.
Host
: (TCP devices only) IP address of slave device from which data is to
be read.
Port
: (TCP devices only) Port on which the slave device will send and
receive modbus traffic. Typically, this will be on port 502.
Address
: Register address of the value you want to read from your Modbus
slave device. Only enter the base portion of the register address (i.e. if the
address is listed as 400100, only enter 100). Note that if the address is
entered in Hexadecimal format, it will be displayed in decimal format the
next time the zone settings page is viewed for that zone.
Command
: Select the appropriate command to issue to the Modbus server
device based on the register type to be read.
(1) Read Discrete Outputs: Use this command to issue a modbus func-
tion code 1 in order to read a discrete output from the Modbus server.
A Discrete Output is a single bit in size (on/off) and may sometimes be
referred to as a “coil”
(2): Read Discrete Inputs: Use this command to issue a Modbus func-
tion code 2 in order to read a discrete input register from a Modbus
server. A discrete input is a single bit data type (on/off).
(3) Read Holding Register: Issue a modbus function code 3 in order to
read a holding register.
(4) Read Input Register: Issue a modbus function code 4 in order to
read an input register.