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HONEYWELL UNITARY CONTROLLER - 230 VAC - INSTALLATION INSTRUCTIONS
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.
MODBUS
UNITARY
SERVER
CONTROLLER
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.
X
MODBUS
UNITARY
SERVER
CONTROLLER
MODBUS
SERVER
MODBUS
SERVER
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.
31-00610-01
MODBUS
SERVER
MODBUS
MODBUS
SERVER
SERVER
MODBUS
SERVER
MODBUS
MODBUS
SERVER
SERVER
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 (120 Ω; the watt-
age should be in the range of 0.25 – 0.5 W).
Modbus Client Specifications
Table 20 Modbus Client Specifications
Specification
2-wire serial line (TIA/EIA-485) (with
Physical Layer
additional common)
Communication
9.6, 19.2, 38.4, 57.6, and 76.8 kbps
supported.
rates
Maximum
32, It is recommended to connect a
numbers of
smaller number of devices for better
Modbus performance.
devices
Cable and
Check cable and specifications in
wiring
power wiring section.
specifications
Communication
Modbus client.
mode
Transmission
RTU (Remote Terminal Unit).
mode
Modbus client can have an address
between 1 and 247.
Address range
Discrete inputs, coils, input registers
and holding registers can have an
address between 1 and 65534.
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.
30
Description
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