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Communication Interfaces - Honeywell CENTRA LINE MERLIN NX Series Installation & Commissioning Instructions

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MERLIN NX ROOM CONTROLLER – INSTALLATION & COMMISSIONING INSTRUCTIONS

COMMUNICATION INTERFACES

Overview of Interfaces
e.g., LIGHT I/O or WALL MODULE
MODBUS
SLAVE
PREVIOUS
MODBUS
CLCM
SYLK BUS
SLAVE
TR40x/TR42x
MODBUS
INTERFACE
RS485-2
INTERF.
RxxN #61
(SLAVE)
AO1
AO2
AO3 AO4
AO5
AO6
24V0
C2+
C2-
GND
24V~
WM1
WM2
32
34
36
38
40
42
(GND)
GND
24V~
GND
24V~
GND
26
27
28
29
30
31
33
35
37
39
41
RxxN #62
(MODBUS MASTER)
1
2
3
4
5
6
7
8
9
L
N
24V~
24V0
24V~
24V0
TN
T~
T01
Fig. 23. System overview (example: RLxN)
The TIA/EIA-485 Standard
According to the TIA/EIA-485 standard ("Electrical Charac-
teristics of Generators and Receivers for Use in Balanced
Digital Multipoint Systems"), only one driver communicating
via an RS485 interface may transmit data at a time. Further,
according to U.L. requirements, each RS485 interface may be
loaded with a max. of 32 unit loads. E.g., Honeywell /
CentraLine devices have as little as ¼ unit load each, so that
up to 128 devices can be connected.
BACnet and Modbus connections to the RS485 interfaces
must comply with the aforementioned TIA/EIA-485 standard.
Thus, it is recommended that each end of every bus be
equipped with a termination resistor (not included in ship-
ment) having a resistance equal to the cable impedance
(120 Ω; the wattage should be in the range of 0.25 – 0.5 W).
RS485 systems frequently lack a separate signal ground wire.
However, the laws of physics still require that a solid ground
connection be provided for in order to ensure error-free
communication between drivers and receivers – unless all of
the devices are electrically isolated and no earth grounding
exists.
IMPORTANT
A separate signal ground wire must be used. Failing to
obey this requirement can lead to unpredictable
behavior if other electrically non-isolated devices are
connected and the potential difference is too high.
TIA-EIA 485 Cable Specifications
The following cable specification is valid for all EIA 485 buses
(incl. Modbus and BACnet MS/TP).
EN1Z-1035GE51 R0420
TCP/IP
BACnet IP
PLANT
CONTROLLER
BACnet WiFi
ADAPTER
RS485-1
BACnet MS/TP
INTERF.
RJ45
24V~
GND
UI2
UI3
GND
UI6
UI7
GND
UI10
C1+
C1- GND
44
46
48
50
52
54
56
58
60
BACnet MS/TP
24V~
LED
UI1
GND
UI4
UI5
GND
UI8
UI9
GND
SERVICE
62
63
64
43
45
47
49
51
53
55
57
59
61
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
TN
T02
T03
TN
T04
RC4
RO4
IN4
RN
RN
IN1
RO1
IN2
RO2
IN3
RO3
Table 9. TIA/EIA 485 cable specifications
max. length
cable type
charac. impedance
distributed capacitance
between conductors
distributed cap. between
conductors and shield
*A higher communication rate (necessitating a shorter max.
length) is possible for Modbus. See section "Modbus
Considerations" on pg. 20.
The following cables fulfill this requirement:
AWG 18;
shielded, twisted pair cable J-Y-(St)-Y 4 x 2 x 0.8;
CAT 5,6,7 cable (use only one single pair for one bus);
Belden 9842 or 9842NH.
BACnet MS/TP Interface
The controller features an isolated RS485 interface (RS485-
1) suitable for BACnet MS/TP communication:
RLxN: terminals 62, 63, and 64;
RSxN: terminals 40, 41, and 42.
The terminal block containing it is gray. The cable length
affects the communication rate. Table 10 provides a few
examples.
Table 10. Baud rate vs. max. cable length
baud rate
9.6, 19.2, 38.4, 57.6, and 76.8 kbps
The controller supports auto-baud rate adaption for BACnet
MS/TP communication at all of the aforementioned baud
rates (default: 38.4 kbps).
For information on wire gauge, max. permissible cable length,
possible shielding and grounding requirements, and the max.
number of devices which can be connected to a bus, refer to
standard TIA/EIA-485.
BACnet MS/TP Considerations
The controller communicates via its isolated RS482-1 inter-
face with other BACnet MS/TP-capable devices (e.g., other
room controllers or plant controllers like the EAGLE / Excel
Web II or EAGLEHAWK NX). In doing so, the following con-
siderations should be taken into account.
Max. BACnet MS/TP bus length (= "L" in Fig. 24): See
Table 10.
Twisted-pair cable, e.g.:
-
AWG 18;
-
J-Y-(St)-Y 4 x 2 x 0.8;
-
CAT 5,6,7 cable – use only one single pair for one
bus;
-
Belden 9842 or 9842NH);
and daisy-chain topology.
18
1200 meters (9.6 – 78.8 kbps)*
twisted pair, shielded (foil or
braided shields are acceptable)
100...130 Ω
Less than 100 pF per meter
(30 pF per foot)
Less than 200 pF per meter
(60 pF per foot)
max. cable length (L)
1200 m

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