ABB FBVi-2U4-4T User manual

—
USER GUIDE
MAN0148 rev 5
FBVi-2U4-4T

©ABB 2021 All Rights Reserved.
Subject to change without notice
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MAN0148 rev 5
Style conventions used in this document:
UI Text: Text that represents elements of the UI such as button names, menu
options etc. is presented with a grey background and border, in Tahoma
font which is traditionally used in Windows UIs. For example:
Ok
Standard Terms (Jargon): Text that is not English Language but instead refers to
industry standard concepts such as Strategy, BACnet, or Analog Input is
represents in slightly condensed font. For example:
BACnet
Code: Text that represents File paths, Code snippets or text file configuration
settings is presented in fixed-width font, with a grey background and
border. For example:
$config_file = c:\CYLON\settings\config.txt
Parameter values: Text that represents values to be entered into UI fields or
displayed in dialogs is represented in fixed-width font with a shaded
background. For example
10°C
Product Names: Text that represents a product name is represented in bold
colored text. For example
INTEGRA™
Company Brand names: Brands that are not product names are represented by
bold slightly compressed text:
ABB Active Energy
PC Keyboard keys: Text representing an instruction to press a particular key on
the keyboard is enclosed in square brackets and in bold font. For
example:
[Ctrl]+[1]

table of contents
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1THE FBVI-2U4-4T
Introduction ...............................................................................................................7
Application..................................................................................................................7
2IP NETWORKING
What is IP? ..................................................................................................................8
Physical Layer (Layer 1)..................................................................................................................................... 8
DataLink Layer (Layer 2)................................................................................................................................... 8
Network Layer (Layer 3).................................................................................................................................... 8
Transport Layer (Layer 4)................................................................................................................................. 8
Session Layer (Layer 5)..................................................................................................................................... 8
Presentation Layer (Layer 6)........................................................................................................................... 8
Applications Layer (Layer 7) ............................................................................................................................ 8
IP Addressing .............................................................................................................9
DHCP (Dynamic Host Configuration Protocol) ......................................................................................... 9
Subnetwork (Subnet)........................................................................................................................................ 9
Default gateway................................................................................................................................................ 10
Port Numbers..................................................................................................................................................... 11
Uplink/WAN and Segmentation .......................................................................... 12
Network Address Translation (NAT)................................................................... 13
Domain Name System (DNS)................................................................................ 13
3BACNET NETWORKING
What is BACnet? ......................................................................................................14
BACnet object types...............................................................................................15
BACnet services.......................................................................................................15
BACnet's Client / Server nature ...........................................................................16
Network Types.........................................................................................................16
PIC Statement..........................................................................................................16
BACnet Topology .................................................................................................... 17
BACnet IP ..................................................................................................................18
BACnet IP Broadcast Management Device (BBMD)................................................................................18
BACnet MS/TP .........................................................................................................19
Token Passing....................................................................................................................................................19
Addressing..........................................................................................................................................................19
Baud Rates .........................................................................................................................................................20
Network Optimization....................................................................................................................................20
BACnet MS/TP Device Loading.................................................................................................................... 20
Read Property Multiple................................................................................................................................... 20
BACnet Priority Array........................................................................................................................................21
4FBVI WEB UI
Summary Dashboard .............................................................................................22
BACnet Menu............................................................................................................23
Device .................................................................................................................................................................. 23
Router Networks .............................................................................................................................................. 23

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Time Sync ........................................................................................................................................................... 24
BBMD / NAT....................................................................................................................................................... 25
IP Network Menu .................................................................................................... 26
Configuration.................................................................................................................................................... 26
TCP/UDP Ports ..................................................................................................................................................27
Edit SSL Cert / Sign SSL Cert ....................................................................................................................... 28
Platform Menu ........................................................................................................ 29
Status report ..................................................................................................................................................... 29
Firmware Upgrade utility............................................................................................................................... 29
Backup/Restore utility....................................................................................................................................30
Set Time and Date ...........................................................................................................................................30
Restart utility ......................................................................................................................................................31
Diagnostics Menu ...................................................................................................32
Processes ........................................................................................................................................................... 32
Debug Level ....................................................................................................................................................... 32
System logs........................................................................................................................................................ 33
Open-source acknowledgment notices .................................................................................................... 33
5INSTALLATION
Apply power to the FBVi-2U4-4T ........................................................................ 34
Connect the FBVi to an IP network .................................................................... 34
The FBVi Integrated Ethernet Switch......................................................................................................... 35
Configuring the IP connection ..................................................................................................................... 35
Wiring the IO ........................................................................................................... 43
Configuring the FBVi-2U4-4T controller........................................................... 45
Setting FBVi-2U4-4T BACnet Commissioning Configuration Codes in CXproᴴᴰ .......................... 45
Input Configuration.........................................................................................................................................46
Heat Setup ......................................................................................................................................................... 47
Heat Order .........................................................................................................................................................48
Digital Hardware Output Configuration ...................................................................................................48
Digital Output Direct/Reverse Action........................................................................................................49
Analog Hardware Output Range Options.................................................................................................49
Analog Output Direct/Reverse Action .......................................................................................................49
6FBVI OPERATION
Physical Layout ....................................................................................................... 50
Inputs and Outputs ................................................................................................52
Input modes ...................................................................................................................................................... 52
Output modes................................................................................................................................................... 55
Auxiliary Power output ......................................................................................... 56
Using a Keypad with the FBVi ..............................................................................57
7FBVI-2U4-4T CONTROL SEQUENCES
FBVI-2U4-4T Common Control sequences ...................................................... 58
VAV Cooling only No Fan ...................................................................................... 58
Temperature Control ......................................................................................................................................58
Input / Output Points..................................................................................................................................... 59
VAV Cooling only Constant Series Speed Fan ................................................. 60
Temperature Control ......................................................................................................................................60
Damper Control................................................................................................................................................60

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Series Single Speed Fan.................................................................................................................................60
Input / Output Points......................................................................................................................................61
VAV Cooling only Variable Series Speed Fan ................................................... 62
Temperature Control ...................................................................................................................................... 62
Damper Control................................................................................................................................................ 62
Series Variable Speed Fan ............................................................................................................................. 62
Input / Output Points..................................................................................................................................... 63
VAV One to Three Stage Electric Reheat No Fan ............................................ 64
Temperature Control ......................................................................................................................................64
Input / Output Points.....................................................................................................................................66
VAV One to Three Stage Electric Reheat Single Speed Fan ..........................67
Temperature Control ...................................................................................................................................... 67
Damper Control................................................................................................................................................ 67
Fan Control ........................................................................................................................................................ 67
Input / Output Points.....................................................................................................................................68
VAV One to Three Stage Electric Reheat Variable Speed Fan...................... 69
Temperature Control ......................................................................................................................................69
Damper Control................................................................................................................................................69
Fan Control ........................................................................................................................................................ 70
VAV Modulating Hot Water Reheat No Fan.......................................................72
Temperature Control .......................................................................................................................................72
Input / Output Points..................................................................................................................................... 74
VAV Modulating Hot Water Reheat Single Speed Fan ....................................75
Temperature Control ...................................................................................................................................... 75
Damper Control................................................................................................................................................ 75
Fan Control ........................................................................................................................................................ 76
Input / Output Points......................................................................................................................................77
VAV Modulating Hot Water Reheat Variable Speed Fan ................................78
Temperature Control ...................................................................................................................................... 78
Fan Control ........................................................................................................................................................ 79
Input / Output Points.....................................................................................................................................80
8CONTROL SEQUENCE OVERVIEW
Occupancy Commands..........................................................................................81
Occupied Mode..................................................................................................................................................81
Unoccupied Mode.............................................................................................................................................81
BACnet Heartbeat communication status and Stand-Alone operation.......................................... 82
HVAC Modes............................................................................................................ 83
Warm-up/Heating State ................................................................................................................................ 83
Cool-down/Cooling State ............................................................................................................................. 83
Heat Only ............................................................................................................................................................ 83
Cool Only............................................................................................................................................................. 83
Fire Stop Command........................................................................................................................................ 83
Purge Command .............................................................................................................................................. 83
Temperature Control ............................................................................................ 84
Heating Mode....................................................................................................................................................84
Cooling Mode....................................................................................................................................................84
Vent Mode ..........................................................................................................................................................85
Setpoint Modifiers...........................................................................................................................................85
CBT Stat.............................................................................................................................................................. 85
CO₂ and Humidity .................................................................................................. 86
CO₂Control ........................................................................................................................................................86
Humidity Monitoring.......................................................................................................................................86

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Window Sensor and Fan Status.......................................................................... 86
Window Sensor.................................................................................................................................................86
Fan Status ..........................................................................................................................................................86
Damper Control ...................................................................................................... 86
Test and Balance .....................................................................................................87
Setting initial box size..................................................................................................................................... 87
Zeroing Airflow sensor ................................................................................................................................... 87
Airflow Calibration Procedure ...................................................................................................................... 87
Scheduling ............................................................................................................... 89
Alarms....................................................................................................................... 89
Low Airflow Alarm............................................................................................................................................89
Low Discharge Air Temperature Alarm......................................................................................................89
Zone Air Temperature Failure.......................................................................................................................89
Discharge Air Temperature Failure.............................................................................................................89
High/Low Zone Air Temperature Alarm....................................................................................................89
Airflow Calibration Alarm...............................................................................................................................89
Leaking Damper Alarm...................................................................................................................................89
Leaking Valve Alarm.........................................................................................................................................89
Fan Alarm............................................................................................................................................................89
High CO₂ Alarm.................................................................................................................................................89
Network Variables.................................................................................................. 90
Network In Variables .......................................................................................................................................90
Unit Status and Graphic Points ...........................................................................91
Unit Status ..........................................................................................................................................................91
Graphic Points....................................................................................................................................................91
Fan Control .............................................................................................................. 93
Parallel Fan ......................................................................................................................................................... 93
Series Fan........................................................................................................................................................... 93
Variable Speed Fan.......................................................................................................................................... 93
Parallel Variable Speed Fan ........................................................................................................................... 93
Series Variable Speed Fan ............................................................................................................................. 93
9APPENDIX: LIST OF FBVI-2U4-4T POINTS
Hardware Points (I/O) .......................................................................................... 94
Analog..................................................................................................................................................................94
Digital ..................................................................................................................................................................94
BACnet Analog Values........................................................................................... 95
BACnet Binary Values ............................................................................................ 99
10 APPENDIX: TROUBLESHOOTING
Controller State .....................................................................................................101
LED Light Indicators.......................................................................................................................................101
Comm Loss.......................................................................................................................................................101
Wired CBT Stat Failure...................................................................................................................................101
Airflow Failure ..................................................................................................................................................101
Damper Failure ................................................................................................................................................101
Fan Failure.........................................................................................................................................................101
Duct Heat Failure.............................................................................................................................................101

FBVi-2U4-4T | The FBVi-2U4-4T
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1 The FBVi-2U4-4T
INTRODUCTION
The FBVi-2U4-4T is a freely programmable BACnet® Unitary Controller with native BACnet/IP
communications support. The controller is BTL listed as BACnet Building Controller (B-BC) and is ideally
suited for the control of Variable Air Volume zoning applications.
Part of Cylon’s FLXeon Series of BACnet/IP field controllers, the FBVi-2U4-4T features 2 UniPuts™, 4
Universal Inputs and 3 Digital (Triac) Outputs, along with an integrated airflow sensor and a dedicated
input for Cylon’s CBT-STAT or other intelligent room sensors. The FBVi-2U4-4T model includes an
integrated Belimo actuator.
FLXeon's scalable and modular architecture utilizes its embedded graphics and visualization engine
FLXvue to get data from the #edge2cloud.
APPLICATION
The FBVi-2U4-4T is suitable for controlling single duct or fan assisted Variable Air Volume (VAV)
applications. This controller also supports demand ventilation application, occupancy sensing or lighting
control to further enhance energy savings.
Examples of typical VAV zoning applications include;
•Cooling only
•Cooling with Reheat
•Cooling with Reheat and Perimeter Radiation
•Series fan VAV
•Parallel fan VAV
The controller accommodates available pre-engineered strategies or can be tailored to custom
applications using CXproᴴᴰ programming software.

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2 IP Networking
WHAT IS IP?
IP (Internet Protocol) is an agreed standard that defines how devices communicate over the Internet or
other Internet-like Ethernet network.
IP is part of a 7-layer architecture consisting of
•Physical Layer (Layer 1)
•DataLink Layer (Layer 2)
•Network Layer (Layer 3)
•Transport Layer (Layer 4)
•Session Layer (Layer 5)
•Presentation Layer (Layer 6)
•Applications Layer (Layer 7)
PHYSICAL LAYER (LAYER 1)
This refers to the electrical impulses (or light signal or radio signals) carried on the cable (or fiber, air or
other physical medium). For IP, the physical layer is usually Ethernet.
DATALINK LAYER (LAYER 2)
This is where data packets are translated to and from bits, which can be transferred on the Physical Layer
NETWORK LAYER (LAYER 3)
Layer 3 provides switching and routing to create paths for data to be transmitted from node to node
within the network. This is the layer that gives IP its name.
TRANSPORT LAYER (LAYER 4)
This layer is responsible for end-to-end error recovery and flow control, enabling transparent transfer of
data between hosts.
SESSION LAYER (LAYER 5)
The Session layer manages exchanges (conversations) between the “applications” on each host.
PRESENTATION LAYER (LAYER 6)
This layer translates between application and network formats, so that communication independent of
data representation such as ASCII, GIF, JPEG etc.
APPLICATIONS LAYER (LAYER 7)
Everything at layer 7 is application-specific, such as Telnet, FTP, WWW browsers, HTTP etc.

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IP ADDRESSING
Each device has at least one IP address, which uniquely identifies it from all other devices on the network.
There are several forms of IP addresses, but the most commonly used is IPv4, which consists of 4
numbers (between 0 and 255 ) separated by dots e.g. 192 . 168 . 222 . 51
DHCP (DYNAMIC HOST CONFIGURATION PROTOCOL)
The address can be set manually on the device itself, or else the device can be assigned one by a master
controller on the network. This master controller is known as the Dynamic Host Configuration Protocol
(DHCP) server.
To use an IP address, a device must know several pieces of data, including the IPv4 address that the
device will use, the IP address of the Domain Name Server (DNS) where the device can find IP addresses
of other devices, and the IP address of the Default Gateway device through which communications are
routed.
Using DHCP means that all these pieces of information are set automatically avoiding the need for
specialist knowledge of IP networking. If DHCP is available on your network is the most convenient way
to configure your devices.
DHCP reservation
A DHCP server can be configured to always assign a particular IP address to a specific device. This is
called a DHCP reservation and enables a user to access a device by IP address even if the device power-
cycles and makes a new DHCP request.
SUBNETWORK (SUBNET)
A subnet is a logical division of a network –that is while it might be physically connected to other
subnets, communications traffic from one subnet can be kept separate from comms origination on
other subnets.
A group of the most significant bits of the IPv4 address (the numbers at the start of the address)
specifies the address of a network or subnetwork. This is called the Network Prefix. The remainder
specifies the host –the address unique to the specific device.
For example:
•on the 192 . 168 subnet, an IP address of 192 . 168 . 2 . 54 refers to device 2 . 54 .
•On the 55 . 231 . 77 subnet, IP address 55 . 231 . 77 . 3 refers to device 3
The specific parts of the address that are in each portion is defined by the device’s ‘Subnet Mask’. This
can be expressed as a “bitmask” that is applied by a bitwise AND operation – e.g. 255 . 255 . 0 . 0 means that
only the last 2 segments of the address apply to the local subnet.
For example,
•if the address 192 . 168 . 2 . 54 has a subnet mask “ 255 . 255 . 0 . 0 ”, that means that 192 . 168 is the subnet
address, and 2 . 54 is the device address.
•if the address 55 . 231 . 77 . 3 has a subnet mask “ 255 . 255 . 255 . 0 ”, that means that 55 . 231 . 77 is the subnet
address, and 3 is the device address.
The network can also be identified by a decimal number following the first IP address on the network –
e.g. 55 . 231 . 77 . 0 / 24 . This is called Classless Inter-Domain Routing (CIDR) notation. The decimal number
represents the number of bits allocated for the Network Prefix.
Each segment of an IP address represents 8 bits,
i.e. 192 . 168 . 2 . 54 could also be written 11000000 . 10101000 . 00000010 . 00110110

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In CIDR notation, /16 means that 16 of these bits represents the subnet, and the remainder specifies the
host:
CIDR
192 . 168 . 2 . 54 / 16
IP
Address
decimal
192
.
168
.
2
.
54
IP
Address
Binary
1
1
0
0
0
0
0
0
.
1
0
1
0
1
0
0
0
.
0
0
0
0
0
0
1
0
.
0
0
1
1
0
1
1
0
16 bits representing the subnet
host
Equivalen
t subnet
mask
255
.
255
.
0
.
0
CIDR
55 . 231 . 77 . 3 / 24
IP
Address
decimal
55
.
231
.
77
.
3
IP
Address
Binary
0
0
1
1
0
1
1
1
.
1
1
1
0
0
1
1
1
.
0
1
0
0
1
1
0
1
.
0
0
0
0
0
0
1
1
24 bits representing the subnet
host
Equivalent
subnet
mask
255
.
255
.
255
.
0
DEFAULT GATEWAY
Devices on the same subnet can address IP packets to each other without using a router device.
To communicate with devices on another subnetwork, the traffic must be routed through a router
device’s WAN port. When a device needs to communicate with an IP address that is not on the same
network, it sends the packet to the Default Gateway, which is usually the subnet’s Router.
Note: Some BACnet services use “broadcasts” (e.g. “Who-Is”). On a LAN with standard routers, these
broadcasts are “blocked”. As a result, BACnet broadcasts are limited to the IP Subnet of the BACnet
device. With a BACnet/IP network of 2 or more IP subnets, a device that can act as a BACnet/IP
Broadcast Management Device (BBMD) must be used.

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PORT NUMBERS
A “Port” on an IP device is a concept that allows traffic to be mapped within a device’s address to a
specific process running in that device. A Port number forms part of a data packet’s IP address, but is
often set by convention, depending on the protocol that the packet uses. For example, HTTP traffic by
convention uses port 80 . If no port is specified in the IP address for HTTP traffic, port 80 will be assumed.
If a port is specified (e.g. port 8080 as in the address 192 . 168 . 100 . 33 : 8080 ), the specified port will be used
instead. This allows the device to communicate on multiple protocols at the same time.
Some of the services associated with port numbers include:
Service
Protocol
Default Port Number
SMTP
TCP
25
DNS
TCP, UDP
53
DHCP
UDP
67
HTTP
TCP
80
HTTPS
TCP
443
BACnet/IP
UDP
47808
Some of the port numbers recognized by FBVi are shown below. These can be changed in the controllers
Web UI at IP Network > TCP/UDP Ports

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UPLINK/WAN AND SEGMENTATION
Physically splitting a network into different function groups is known as “Network segmentation”. This is
done to improve performance (by reducing the amount of traffic on each segment) and to improve
security. It is achieved by connecting Routers together by their “WAN” or “UPLINK” ports.
If routers are connected without using their “WAN” or “UPLINK” ports, the result is a single segment:

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NETWORK ADDRESS TRANSLATION (NAT)
Network Address Translation is a function of a router or firewall, which maps multiple local IP addresses to
a single public IP address. This is necessary because the number of IPv4 addresses is finite.
DOMAIN NAME SYSTEM (DNS)
When communicating on the wider Internet, it can be difficult to remember the numeric IP address for
each device with which you want to communicate. The Domain Name System (DNS) was created to allow
internet users to use a text-based Uniform Resource Locator (URL) with meaningful values such as
“www.cylon.com” to connect to a site or device without having to know the server’s IP address. The DNS
finds the URL in its distributed database and passes the corresponding numeric IP address to the
requesting device. If a device’s IP address changes, the DNS server can be updated with its new IP
address, ensuring that other networked devices can still find this device from its URL.
When setting a devices IP parameter manually, between one and three DNS IP address are usually
provided. The second and third addresses are used if the first DNS becomes unavailable.
If you do not know the address of your DNS server(s), you can use publicly available DNS server addresses
for example primary = 8.8.8.8 and secondary = 4.4.4.4

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3 BACnet Networking
WHAT IS BACNET?
BACnet is "a data communication protocol for building automation and control networks." This means it
is a set of rules for exchanging BMS information between systems from different manufacturers.
The rules take the form of a written specification that spells out what is required to conform to the
protocol
The key feature of BACnet is that the rules relate specifically to the needs of building automation and
control equipment - for example, how to ask for the value of a temperature, define a fan operating
schedule, or send a pump status alarm.
BACnet provides a standard way of representing the functions of any device - for example analog or
binary inputs or outputs, schedules, control loops and alarms.
The standardized model of a device represents these common functions as collections of related
information called objects
Each object has a set of properties that further describe it. Each analog input, for instance, is
represented by a BACnet "Analog Input object", which has a set of standard properties such as 'Present
Value', 'Sensor Type', 'Location', 'Alarm Limits' etc. Some of these properties are required, while others are
optional.
The only required object in each BACnet controller is the Device object. This object contains the
properties that define the controller’s behavior on the network. Each controller’s Device object has an
associated number called the Device Instance. It is this unique number that allows all other BACnet
devices to unambiguously access the controller.
Here is an illustration of BACnet objects:

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BACNET OBJECT TYPES
The BACnet standard defines a number of standard object types, and this number is increasing over time.
Cylon uses the following standard types (* indicates that the object is proprietary):
•Device
•Analog Input
•Analog Value
•Analog Output
•Binary Input
•Binary Value
•Binary Output
•Schedule
•Calendar
•Unitron Schedule *
•Notification Class
•File
•Trend Log
•Manufacturing Object *
BACNET SERVICES
The BACnet standard defines numerous services for interaction between BACnet devices. The following
are supported by Cylon BACnet products:
•ReadProperty
•WriteProperty
•ReadPropertyMultiple
•WritePropertyMultiple
•Read Range
•WhoIs
•IAm
•WhoHas
•IHave
•UnconfirmedPrivateTransfer
•TimeSynchronization
•UTCTimeSynchronization
•DeviceCommunicationControl
•ReinitializeDevice
•AtomicWriteFile
•AtomicReadFile
•AcknowledgeAlarm
•GetAlarmSummary
•GetEventInformation
•ConfirmedEventNotification
•UnconfirmedEventNotification
•SubscriveCOV
•ConfirmedCOVNotification
•UnconfirmedOVNotification

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BACNET'S CLIENT / SERVER NATURE
BACnet uses a “Client/Server" architecture. BACnet messages are called service requests. A Client machine
sends a service request to a Server machine that then performs the service and reports the result to the
Client.
Example:
A simple device such as a fixed function VAV controller would typically act as Server.
Front-end software running on a PC would act as a BACnet Client reading status values from the VAV and
changing set-points.
Notes:
Server devices cannot initiate communication. Higher end embedded controllers generally include both
server and client functionality. This allows them to share information such as outside temperature with
each other or send alarms to a PC.
BACnet currently defines 35 message types that are divided into 5 groups or classes. For example, one
class contains messages for accessing and manipulating the properties of the objects described above.
A common message type is the "ReadProperty" service request. This message causes the server
machine to locate the requested property of the requested object and send its value back to the client.
Other classes of services deal with: alarms and events, file uploading and downloading, managing the
operation of remote devices and virtual terminal functions.
NETWORK TYPES
BACnet messages can be carried over the following types of network:
•Ethernet
•ARCnet
•Master-Slave/Token-Passing (MS/TP)
•Point-to-Point (PTP)
•LON
•BACnet/IP
PIC STATEMENT
Every BACnet device is required to have a "protocol implementation conformance statement“ (PICS). A
PICS is a BACnet specification sheet, containing a list of a device's BACnet capabilities.
It contains:
•a general product description
•details of a product's BACnet capabilities
•which LAN options are available
•a few other items relating to character sets and special functionality
The PICS is the place to start to see what a device's capabilities are.

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BACNET TOPOLOGY
A typical BACnet Network consists of devices connected to physical networks. Each device is a separate
piece of hardware and has a physical connection to the network. Devices are given a unique Device
Instance Number which can be a number between 0 and 4194302. BACnet MS/TP devices have additional
addressing designations called MAC addresses. For most users it is the Device Instance Number which is
used as a reference, but the combination of the Network Number and MAC address of an MS/TP device
may be configured by a System Integrator to avoid any MAC address conflicts on the EIA-485 network.

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BACNET IP
BACnet/IP uses the User Datagram Protocol (UDP) to send data packets. ASHRAE adopted BACnet/IP
in annex j of the 135- 1995 standard.
BACnet/IP communicates using four methods.
•BACnet/IP to BACnet/IP (same subnet): Assuming that two devices know each other's IP
addresses and the UDP ports they are using, i.e., their respective B/IP addresses, there is nothing
that restricts them from communicating directly.
•BACnet/IP to BACnet/IP (different subnet): The location of the two devices is already known by
the host and the message is routed to the device using switches and routers.
•Broadcast (same subnet): This is a standard Who is/ I am message sent across a local subnet for
the BBMD to discover what the address are for the BACnet devices on the subnet.
•Broadcast (different subnet): This is a standard Who is/ I am message sent across a local subnet
for the BBMD to discover what the address are for the BACnet devices on other subnets.
BACNET IP BROADCAST MANAGEMENT DEVICE (BBMD)
Some BACnet services use “broadcasts” (e.g. “Who-Is”). On a LAN with standard routers, these
broadcasts are “blocked”. Thus, BACnet broadcasts are limited to the IP Subnet of the BACnet device.
With a BACnet/IP network of 2 or more IP subnets, a device with BBMD can be used.
A BBMD located on an IP subnet monitors the origin of a broadcast message on that subnet and, in turn,
constructs a “peer to peer” message in order to pass through an IP router. This “peer to peer” message is
received by other BBMDs on other IP subnets and transmitted as a broadcast on their attached subnets.
Since the BBMD messages are directed messages, individual messages must be sent to each BBMD. Each
BBMD device maintains a Broadcast Distribution Table (BDT) , the content of which is usually the same for
all BBMDs within the network. BBMDs must know the IP address of all other BBMDs in the network.
It is possible to communicate to a device on a subnet that does not have a BBMD as in the BACnet
Workstation example above. This type of device is called a foreign device since it resides on a different IP
subnet from devices attempting to communicate with it.
Usually, in BACnet/IP, a foreign device is on a different subnet.
The foreign device (e.g. BOWS) registers with each BBMD, after which it can communicate with all other
devices on the network. The BBMD then maintain a Foreign Device Table (FDT) which keeps track of
foreign devices.

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BACNET MS/TP
Note: FBVi is IP only, this section is provided for general information.
BACnet MS/TP (Master-Slave Token Passing) is an EIA-485 network layer intended for use with lower-level
devices such as Unitary Controllers. In comparison to BACnet/IP and BACnet/Ethernet, MS/TP is more
cost-effective to implement due to the lower cost of wiring. Given the MS/TP network is a serial-based
network, devices may be configured to communicate at different baud rates specified by BACnet.
Therefore, it is essential to know information regarding the BACnet network you are connecting to
before installing.
TOKEN PASSING
BACnet MS/TP uses token passing to allow devices to communicate on the network. Token passing is
controlled by each device, which contains an internal memory list of other MS/TP peers connected to the
network. The token is passed in order of the MAC Address (Unit ID) from lowest to highest. In most
MS/TP networks, each device is configured to be a master. Given all devices may be a master, MS/TP may
appear and react slower than traditional building automation protocols. However, configuring your
network for faster baud rates will help provide better bandwidth and transport speed of network
messaging.
Token passing is a communications scheme that allows connected devices connected to
intercommunicate with one another. A network “token” is passed from unit to unit on the network in a
round-robin fashion by order of the MAC Address (lowest to highest) to provide a transport to access the
network. When a unit possesses the token, it may perform any network activity for which it is
responsible. When finished, the token is then passed onto the next device. At any time, the unit that
possesses the token is the only device permitted to initiate communications with another device on the
network or to request information from it. A device that receives the token may or may not need to
perform network functions (e.g. read values from a remote device, broadcast information, etc.). If not, it
will simply pass the token along the network.
If you are connecting devices to an existing MS/TP network consisting of third-party devices, consult
third-party vendor documentation regarding MS/TP network considerations.
ADDRESSING
BACnet MS/TP devices contain two device addresses. One device address is known as a Device Instance,
and the other is a MAC Address. The Device Instance is an address assignment that is used to identify the
BACnet device on a global BACnet network. When a device is connected to a global BACnet network
consisting of multiple data layers joined together using routers, the Device Instance is used to uniquely
identify the device on a global basis. The valid range for the device instance in a BACnet device is 0 to
4,194,302. Devices must be configured for a unique, non-conflicting Device Instance. In the event that
multiple devices are assigned the same Device Instance, both devices will simply not communicate on the
BACnet network or could be subject to misdirected messaging (a message intended for Device-A may be
routed to Device-B)
The MAC Address is an address assignment used within the BACnet MS/TP segment to permit a device
to actively communicate on the BACnet MS/TP network. Valid MAC Address assignments range from 0 to
127 and are typically assigned in a logical and incremental order to permit faster token passing between
devices. The MAC Address of a BACnet MS/TP device must be a unique, non-conflicting value that exists
on the local MS/TP network. In the event that multiple devices are assigned with the same MAC Address,
the effects can be far detrimental than that of a conflicting Device Instance; potentially resulting in a
failure of the entire local MS/TP network. In the event that the unitary controller encounters a duplicate
of its MAC Address, devices will inform the user that a duplicate MAC Address has been detected and will
not perform client communications until resolved.

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BAUD RATES
As a serial-based protocol, BACnet MS/TP supports the following four baud rates: 9.6kbps, 19.2kbps,
38.4kbps, and 76.8kbps. Devices can be configured for any of these baud rates, as well as native PC baud
rates 57.6kbps and 115.2kbps which are currently not supported by the BACnet standard. Each device
communicating on an MS/TP network must be configured for the same baud rate at all times
NETWORK OPTIMIZATION
In BACnet MS/TP devices, specific device properties are available to permit optimization. Network
communications. By adjusting Device properties max-master and max-info-frames, users can adjust the
token passing abilities of devices. The functionality of these two properties is described as follows:
• Max-Master - defines the highest unit ID of an MSTP master that is connected to the network. This
value specifies to what address extent a token may pass. For example, if you have 64 devices
addressed in a logical order, this value would be assigned to 64. This value should be set to the same
value across all devices connected to an MSTP network.
• Max-Info-Frames - defines the number of data frames that an MSTP master can use the token before
passing onto the next device. This value is typically set by the factory but can be modified if necessary.
In the event a device does not need to keep the token for the number of frames specified, devices will
automatically pass the token onto the next device.
BACNET MS/TP DEVICE LOADING
MS/TP (Master-Slave Token Passing) is a protocol where each device is wired in series and they take
turns communicating, depending on which device currently holds a “token”. It is a robust design, and
simpler/cheaper than IP though less flexible in terms of interoperability.
BACnet MS/TP is widely used in building automation, and usually uses RS-485 networking. As a result, the
number of devices that can be connected together (on a “trunk” or “Fieldbus”) is limited by the electrical
load the device puts on the network.
Unit Load is a concept created by the RS-485 specification to help determine how many devices can be
connected to each fieldbus. The number of devices that can be connected depends on how much each
device loads the fieldbus so the more a device loads the fieldbus, the fewer additional devices can be
used. The total Unit Loads on a fieldbus must be 32 or less.
BACnet MS/TP allows 127 master device addresses, but the Unit Loading usually prevents that number of
devices being active on a fieldbus.
READ PROPERTY MULTIPLE
A single BACnet request can contain a sequence of BACnet property references, each representing a
single BACnet property. This allows multiple properties to be read with a single BACnet request.
By default, FBVi will read 5 properties at once.