MERLIN NX IP AND MST/TP VAV CONTROLLER - INSTALLATION INSTRUCTIONS
EN1Z-1076GE51 R0722
24
1.
Find an unused MAC address on the MS/TP network to
which the MERLIN NX MS/TP VAV controller connects.
2.
Locate the DIP switch bank on the MERLIN NX MS/TP VAV
controller BACnet for addressing.
3.
Powered off the MERLIN NX MS/TP BACnet Controller and
set the DIP switches for the MAC Address you want.
Add the value of DIP switches set to ON to determine the
Table 8, “DIP Switch Values For
MS/TP MAC Address,” on page 24
below.
For example, if only DIP switches 1, 3, 5, and 7 are enabled
the MAC address would be 85 (1 + 4 + 16 + 64 = 85).
Fig. 30. Calculating the MAC address
Setting the Device Instance Number
The Device Instance Number must be unique across the
entire BACnet system network because it is used to
uniquely identify the BACnet devices. It may be used to
conveniently identify the BACnet device from other devices
during installation. The MERLIN NX MS/TP BACnet
Controllers Device Instance Number is automatically set
when it is added to a ARENA-NX project. The Device
Instance Number can be changed by the user, which may
be necessary when integrating with a third party or when
attempting to replace an existing controller and it is desired
to maintain the existing Device Instance Number.
NOTE:
This controller is insensitive to bias voltages because
of failsafe chip-set inside and can share the BACnet
bus with other devices with or without bias voltages.
Connecting to BACnet MS/TP Buses
The controller communicates via its BACnet MS/TP
interface with other BACnet MS/TP-capable devices (for
example, other room controllers or MS/TP controllers). In
doing so, the following considerations should be taken into
account.
— Maximum BACnet MS/TP bus length = "L" on
Fig. 18 See Table 7, “Baud rate vs. Maximum cable
— Twisted-pair cable, for example,
• AWG 18 (1 mm2)
• J-Y(ST)Y 4 x 2 x 0.8 mm2 or a special RS485 cable.
• CAT 5,6,7 cable – use only one single pair for one bus
• Belden 9842 or 9842NH and
• Daisy-chain topology.
• Must conform to TIA/EIA RS485 cabling guidelines and
ANSI/ASHRAE Standard 135-2010.
BACnet MS/TP Limitataions
There are two limitations regarding the number of
controllers per BACnet MS/TP channel:
PHYSICAL LIMITATION:
32 loads as per TIA/EIA-485 standard. One MERLIN NX
MSTP VAV controller represents 1/8 load. The physical
limitation is important in case 3rd party devices
representing a full load are connected.
AUTOMAC LIMITATION:
See Table 7, “Baud rate vs. Maximum cable length,” on
for default maxmaster value. It can be modified by
the user. Refer
IRM Engineering Tool
User Guide
for more
information on how to do this?
A maxMaster of 64 means we can support a maximum of
62 BACnet MSTP VAV controllers, one supervisor, and one
BACnet client (tool) per BACnet MS/TP channel.
Thus, depending upon the actual performance needs and
required communication rates, it is recommended to
connect a smaller number of BACnet MS/TP devices per
channel.
NOTE:
It is recommended not to have more than 62 control
-
lers on single MSTP channel.
Table 8. DIP Switch Values For MS/TP MAC Address
DIP
1
2
3
4
5
6
7
VALUE
1
2
4
8
16
32
64
1
4
3
2
5
7
6
ON
1
4
16
64
+
+ +
= 85
0
+ +
0
0
+
