HONEYWELL UNITARY CONTROLLER - 230 VAC - INSTALLATION INSTRUCTIONS
31-00610-01 30
MODBUS RTU
The controller features a removable 2-wire with shield,
non-isolated, RS-485 interface suitable for Modbus
communication (terminals 45, 46, and 47). The terminal
block containing it is gray. The controller can function
only as a Modbus client. In general, the TIA/EIA 485
wiring rules must be followed.
Wiring Topology
Only daisy chain wiring topology is allowed.
Fig. 29 Modbus Wiring Topology
Other wiring topologies (such as star wiring and mixed
star wiring) are prohibited. This is to avoid
communication problems in the physical layer.
Fig. 30 Prohibited Wiring Topology (example)
Cables and Shielding
Use shielded twisted pair cable J-Y-(St)-Y 4 x 2 x 0.8 and
connect the Modbus shield to a noise-free earth ground
(only once per Modbus network).
Shielding is especially recommended when the Modbus
cable is installed in areas with expected or actual
electromagnetic noise. Prefer avoiding such areas.
You must use three wires:
• One wire for Modbus +
• One wire for Modbus –
• One wire for the shield termination
When using one pair for Modbus (+) and Modbus (-) and
one wire of another pair for the shield termination,
CAT5 cable may also be used.
Modbus RS-485 Repeaters
RS-485 repeaters are possible but have not been tested
by Honeywell; therefore, it is the installing or
commissioning person's responsibility to ensure proper
operation.
NOTE:
Each Modbus segment will require its own line
polarization and line termination (120Ω; the watt-
age should be in the range of 0.25 – 0.5W).
Modbus Client Specifications
Table 20 Modbus Client Specifications
Modbus Compliance
As per the Modbus standard, the Unitary controller is a
conditionally compliant “regular” Modbus device.
The controller differs from an unconditionally
compliant “regular” Modbus device in that it does not
support communication rates of 1.2, 2.4, and 4.8 kbps
(because these communication rates are not market-
relevant).
The baud rates (1200, 2400, 4800, 9600, 14400, 19200,
38400, 57600, 115200), parity (Even/Odd, None) and
the number of stop bits (1 or 2) can be selected under
Controller > IRM Program > Control Manager.
UNITARY
CONTROLLER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
UNITARY
CONTROLLER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
MODBUS
SERVER
Specification Description
Physical Layer
2-wire serial line (TIA/EIA-485) (with
additional common)
Communication
rates
9.6, 19.2, 38.4, 57.6, and 76.8 kbps
supported.
Maximum
numbers of
devices
32, It is recommended to connect a
smaller number of devices for better
Modbus performance.
Cable and
wiring
specifications
Check cable and specifications in
power wiring section.
Communication
mode
Modbus client.
Transmission
mode
RTU (Remote Terminal Unit).
Address range
Modbus client can have an address
between 1 and 247.
Discrete inputs, coils, input registers
and holding registers can have an
address between 1 and 65534.