Honeywell EC350 - Modbus Communication

7 Remote Communications
7.3 Modbus Communication
Honeywell 2024
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7.3 Modbus Communication
Modbus is a common industrial communication protocol. The EC350 supports the Modbus protocol (as a
slave device) on the TB4 RS-232/485 port as well as the front panel IrDA port. Through the RS-232/485
port it can also be used with modems including Messenger, CNI2, and CloudLink 4G/ CloudLink 4G M1
(except CloudLink 5G modem which communicates through the IO Port, i.e. UART). Function codes 01, 02,
03, 04, 05, 06, 15 and 16 are supported, in both RTU and ASCII modes.
The Modbus protocol standard defines the format of the data and the techniques used to control the flow
of data. It supports one master device and up to 247 slave devices on one bus (although a maximum of 32
slave devices are permitted on an RS-485 network, due to physical layer limitations). The master always
initiates a communication exchange. Each slave on a Modbus network has its own unique address
(1...247) so that it can be addressed independently from other slaves. This address is sent by the master
as part of every message. All slaves on the network see the message, but only the slave with the matching
address will respond to the message. A message sent to a slave from the master is called a request, the
answer sent back to the master is called a response. Request and response messages are also called
packets or frames. The master can also broadcast a message to all slave devices, using a slave address of
0. In that case there is no response.
Modbus configuration items are found in the ‘Modbus Protocol’ and ‘Modbus Map Registers’ function
groups of MasterLink Software Application :
If the external device communicates via Modbus protocol, item 985 must be set to 1. Item 994 will need to
be set to the proper Modbus variation, either RTU or ASCII. The correct setting for all of these items will be
determined by the external device used.
Modbus registers can be ‘mapped’ to items in the EC350 via the items in the following group. For
example, pressure can be mapped to register 7003 by enabling Float mapping in item 935 and setting
item 943 to ‘8’.