BACnet-Protocal-Learn

Part 1 - Theory about BACnet

What is Bacnet

This post has ZERO intention to cover the details for the technology. It solely served as learning notes for potential BACnet COMM module development in LabVIEW development.

The BACnet is abbreviation for Building Automation and Control Network and it is both an international (ISO) and ANSI standard for interoperability between cooperating building automation devices.BACnet addresses the goal of interoperability by defining a generalized model of how automation devices work, a method for describing the information that they contain, and a method for describing protocols that one device can use to ask another device to perform some desired action.

BACnet uses an object-oriented model for abstracting and representing information.The object-based model has been proven to be both robust and reliable while providing a high degree of backward and forward complatibility.

In general, two types of networking options are used. There are no proprietary chip sets or special electronics required to implement. Thus, BACnet meets the needs of users, integrators, and equipment vendors. BACnet defines a set of standard objects whose properties represent the information that is exchanged between components of the system network and an application layer protocaol that is used to access and maniplulate this information.

• BACnet serial MSTP
• BACnet/IP network

The communication protocal consists a set of rules that monitors data that is exchanged between devices, enubale communication among devices in a network.

To communication between devices, the BACnet protocal uses services and objects. One device could have a collection of objects and each object has a collection of properties. Each property includes at least a name and a value. For example one of the standard BACnet objects is the Analog Input Object which represents an analog sensor input such as a thermistor.

Below diagram of an Analog Input Object that includes Description, Device_Type, Units are set during installation. Others, including Present_Value and Out_Of_Service provides status about the sensor input represent by the Analog Input Objects. An Analog input object can have up to 25 properties. in this example, a query about the Present_Value Property of this Analog Input Object would get the reply “68.0”.

• Devices

  A BACnet device is often comprised of a microprocessor-based controller and software combination is the designed to undertand and use the BACnet protocal. Each device contains a device object (and other objects) that defines certain device information including the device object identifier or instance number. The instance number must be field-configurable to be unique across the entire BACnet network. For brevity this number called device instance.

  BACnet requires one Device Object to be present in every BACnet device.he Device Object’s Instance number must be unique across the entire BACnet internetwork 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.

  Properties of the Device Object.

PROPERTY	BACnet	EXAMPLE
Object_Identifier	Required	Device #1076
Object_Name	Required	“Office 36 DD Control”
Object_Type	Required	Device
System_Status	Required	Operational (plus others)
Vendor_Name	Required	“Alerton Technologies, Inc.”
Vendor_Identifier	Required	Alerton
Model_Name	Required	“VAV-DD Controller”
Firmware_Revision	Required	“1.0”
Application_Software_Version	Required	“Dual-Duct DDC”
Location	Optional	“Office 36, Floor 3”
Description	Optional	“(on network 5)”
Protocol_Version	Required	1 (BACnet protocol version)
Protocol_Conformance_Class	Required	2
Protocol_Services_Supported	Required	readProperty, writeProperty, atomicWriteFile,…
Protocol_Object_Types_Supported	Required	Analog Input, Analog Output,…
Object_List	Required	Analog Input #1, Analog Input #2, …
Max_APDU_Length_Supported	Required	50 (bytes or characters)
Segmentation_Supported	Required	No
VT_Classes_Supported	Optional	n/a
Active_VT_Sessions	Optional	n/a
Local_Time	Optional	12:30:15.22
Local_Date	Optional	Tuesday, March 12, 1996
UTC_Offset	Optional	+480 (minutes from GMT/UTM)
Daylight_Savings_Status	Optional	False (not in effect)
APDU_Segment_Timeout	Optional	n/a
APDU_Timeout	Required	3000 milliseconds
Number_Of_APDU_Retries	Required	0
List_Of_Session_Keys	Optional	n/a
Time_Synchronization_Recipients	Optional	n/a
Max_Master	Optional	n/a
Max_Info_Frames	Optional	n/a
Device_Address_Binding	Required	None

• Devices Interoperability BACnet divides the task of device interoperability into three distinct areas: Objects (information), Services (action requests), and Transport systems (internetworking, electronic messages). BACnet defines methods and requirements for implementation of each of these areas

• Object BACnet devices are defined on the network as a collection of “objects”. The BACnet standard defines 54 different standard object types and implementation of a given device may make use of arbitrary combinations of these standard object types to represent information and control logic.

  Each oject is identified with an object identifier and an object identifier is a 32-bit binary number. The general reference to sensors, actuators, and other functional elements that make up a BACnet device. The objects fall into categories specified by BACnet protocol. Analog Input object and Analog Ouput object are a couple of the most commonly used objects.

Standard BACnet Objects

OBJECT	EXAMPLE OF USE
Analog Input	Sensor input
Analog Output	Control output
Analog Value	Setpoint or other analog control system parameter
Binary Input	Switch input
Binary Output	Relay output
Binary Value	Binary (digital) control system parameter
Calendar	Defines a list of dates, such as holidays or special events, for scheduling.
Command	Writes multiple values to multiple objects in multiple devices to accomplish a specific purpose, such as day-mode to night-mode, or emergency mode.
Device	Properties tell what objects and services the device supports, and other device-specific information such as vendor, firmware revision, etc.
Event Enrollment	Describes an event that might be an error condition (e.g., “Input out of range”) or an alarm that other devices to know about. It can directly tell one device or use a Notification Class object to tell multiple devices.
File	Allows read and write access to data files supported by the device.
Group	Provides access to multiple properties of multiple objects in a read single operation.
Loop	Provides standardized access to a “control loop.”
Multi-state Input	Represents the status of a multiple-state process, such as a refrigerator’s On, Off, and Defrost cycles.
Multi-state Output	Represents the desired state of a multiple-state process (such as It’s Time to Cool, It’s Cold Enough and it’s Time to Defrost).
Notification Class	Contains a list of devices to be informed if an Event Enrollment object determines that a warning or alarm message needs to be sent.
Program	Allows a program running in the device to be started, stopped, loaded and unloaded, and reports the present status of the program.
Schedule	Defines a weekly schedule of operations (performed by writing to specified list of objects with exceptions such as holidays. Can use a Calendar object for the exceptions.

• Object Property

  Each object has/includes several properties required by BACnet protocol.Each property contains two pieces of information.

  • Property Identifier
  • Property Value

  The messages on the network deal with reading and writing Object Properties. The most commonly used protperty is Present Value. An object along with its set of properties describes the current status of a device to the other devices on the network. Objects enable ,reading, writing and perform the desired functions of a device.

• Analog Input
• Analog Output
• Analog Value
• Binary Input
• Binary Output
• Device
• etc.

Properties of the Analog Input Object.

PROPERTY	BACnet	EXAMPLE
Object_Identifier	Required	Analog Input #1
Object_Name	Required	“AI 01”
Object_Type	Required	Analog Input
Present_Value	Required	68.0
Description	Optional	“Outside Air Temperature”
Device_Type	Optional	“10k Thermistor”
Status_Flags	Required	In_Alarm, Fault, Overridden, Out_Of_Service flags
Event_State	Required	Normal (plus various problem-reporting states)
Reliability	Optional	No_Fault_Detected (plus various fault conditions)
Out_Of_Service	Required	False
Update_Interval	Optional	1.00 (seconds)
Units	Required	Degrees-Fahrenheit
Min_Pres_Value	Optional	-100.0, minimum reliably read value
Max_Pres_Value	Optional	+300.0, maximum reliably read value
Resolution	Optional	0.1
COV_Increment	Optional	Notify if Present_Value changes by increment: 0.5
Time_Delay	Optional	Seconds to wait before detecting out-of-range: 5
Notification_Class	Optional	Send COV notification to Notification Class Object: 2
High_Limit	Optional	+215.0, Upper normal range
Low_Limit	Optional	-45.0, Lower normal range
Deadband	Optional	0.1
Limit_Enable	Optional	Enable High-limit-reporting, Low-limit-reporting.
Event_Enable	Optional	Enable To_Offnormal, To_Fault, To_Normal change reporting.
Acked_Transitions	Optional	Flags indicating received acknowledgments for above changes.
Notify_Type	Optional	Events or Alarms

• Service

  BACnet services are formal requests that one BACnet device sends to another BACnet device to ask it to do something. A service is a means or interface between two devices to access and process information, request to perform an action, or inform the devices that some event has taken place. These are used for discovering devices and objects, and for sharing data. BACnet protocol defines “services”. These include object access services, alarm and event services, file access services, and a few more. Object access services are the most commonly used since these provide the fundamental “read/write” access to object properties Some services example

  • Who-Is (Device and Object Discovery)
  • I-Am (Device and Object Discovery)
  • etc. The model of objects and services is realized by encoding messages into a stream of numeric codes that represent the desired functions or services to be performed. d. The “language” of this encoding is common to all BACnet devices. BACnet devices exchange information and do things by sending and receiving electronic messages containing this coded language.

Addressing

Baud Rate

Baud Rate is the rate at which data is communicated to the devices. You can configure the MS/TP networks to communicat at the following baud rates:

• 9.6 kbps
• 19.2 kbps
• 38.4 kbps
• 76.8 kbps
• Auto Detect

All the devices on the MS/TP segment must communicate at the same band rate.

Device ID & Device Instances

The Device ID (Device Object Identifier) is used in a BACnet network as the unique identifier of a specific device. The Device ID for each device must be unique on the entire BACnet network.

This is the logical address that matters to BACnet. Whether on an MS/TP link or IP network, the device instance is unique across all subnets and routed links. Device Instance can be in the range of 0 to 4194304(?). The device instance can be set via the device display or BACnet.

MAC Addresses

The MAC address must be unique on a BACnet MT/TP segment. By default, the MAC address on our controllers is set to 0. A MAC address cannot be duplicated on a single MS/TP trunk. The MAC address can be set via onboard DIP switches, the device display or via BACnet.

Master - Slave

MS/TP stands for Master Slave Token Passing. Each device on the link is considered the “master” when it has the token. If it does not have immediate need to use the token, it is required to pass the token along to the next device. This is the “token passing” part. All devices on the link, which do not currently have the token are regarded as slaves, and are expected to listen to any messages the current master may have for it. Because all devices take turns being master, the link is effectively peer-to-peer.

0-127 addresses are for master devices and 128-254 addresses are reserved for slave devices. Only master devices can initiate requests and are part of the token passing. Slave devices cannot initiate requests for data,they only reply to messages from other master devices and are not part of the token passing.

Part 2 - Edigit BACnet API

Help link https://endigit.com/bacnet-labview-api/detailed-help

Design

1. Function as a device on a BACnet serial MSTP or BACnet/IP network (replies to Who-Is with I-Am)
2. Read/write Present Value for Analog/Binary Input/Output/Value object types
3. Issue Change of Value (COV) requests to reduce network usage

Implementation

The Endigit BACnet API is a class-based LabVIEW driver that follows the “Initialize -> Read/Write -> Close” model.

You will initialize the main class based on the type of BACnet device you want to be (BACnet/IP, MSTP Master, or MSTP). This initialization will return the light blue class wire, which you will use for any reads and/or writes, and finally for the close. This initialize call spins up dynamic loops to handle the device (UDP for BACnet/IP and EIA-485 serial for MSTP) and APDU (Application Layer Protocol Data Unit) layers.

You will also need to initialize a BACnet object for each object you want to talk to using “Object.lvclass:Initialize B.IP Object.vi” or the generic “Object.lvclass:Initialize.vi”. The class returned from this initialize will be an input to any reads or writes.

“IP Address” is the local IP address you want the UDP connection to be opened on.

“Local Port (0xBAC0)” is the local port you want to use to create the UDP socket. The default is 0xBAC0, but this can be any available port. You will receive messages and replies from other devices on this port.

“Instance (7)” (optional) uniquiely identifies this device object from other device objects at this IP address and port. This is up to you to define. Doesn’t much matter because only one device can be on a given UDP port anyway.

“Object Name” (optional) is inserted into the “object_name” property of the device, which may be read by other devices.

“Objects” (optional) is an array of objects that you want this device to own. If you are wanting to host objects and values for other devices to read/write from/to, then initiaize them using “Object.lvclass:Initialize.vi” and pass them in here.

“BACnet Out” (output) is the BACnet class used for all other API methods.

“VISA” is the reference to the serial port you want your device to reside on.

“Baud Rate” is the defined baud rate for the serial network you are connecting to.

“Address” uniquely identifies your device on the serial network. Must not collide with any other devices on the network.

“BACnet Out” (output) is the BACnet class used for all other API methods.

“Remote IP Address” is the IP address of the device you want to read from or write to.

“Type” is the type of the object you want to read from or write to. Tested types with this API are Analog/Binary Input/Output/Value. You will need to get this from your specific BACnet configuration.

“Instance” uniquiely identifies the object of a given type at the specified address. You will need to get this from your specific BACnet configuration.

“Remote Port (0xBAC0)” is the port on the remote device you want to read from and write to. You can have multiple objects on a port and multiple ports on a device. You will need to get this from your specific BACnet configuration.

“Write Priority (0)” (optional) defines the relative priority of objects for arbitration. Valid options are 1-16, with 1 being the highest priority. A ‘0’ will cause the property to not be written (less bandwidth usage), defaulting the priority to a 16.

“Object Out” (output) is the BACnet object used in the read and write methods

“BACnet In” is the BACnet class and it must be initialized before being called here.

“Object In” is the object you want to write to. See “Initialize B.IP Object”.

“Property (Present Value)” is the property of “Object In” that you want to write to. This enum contains all of the properties in the BACnet specification, but only Present Value has been thoroughly tested.

“Value” is the value you want to write to the object property. For analogs, this gets converted to a single. For booleans, 0 is false, everything else is true.

“Timeout (10000 ms)” (optional) defines the maximum time to wait for a reply. If no reply is received by this time, the VI returns a timeout error.

“BACnet Out” (output) is the BACnet class used for all other API methods.

“BACnet In” is the BACnet class and it must be initialized before being called here.

“Object In” is the object you want to read from. See “Initialize B.IP Object.vi”.

“Property (Present Value)” is the property of “Object In” that you want to read from. This enum contains all of the properties in the BACnet specification, but only Present Value has been thoroughly tested.

“Timeout (10000 ms)” (optional) defines the maximum time to wait for a reply. If no reply is received by this time, the VI returns a timeout error.

“BACnet Out” (output) is the BACnet class used for all other API methods.

“Value” (output) is the value of the property that you read from

“BACnet In” is the BACnet class used for all other API methods. Each initialized instance should be closed when it is no longer needed.

Part 3 - Example Demo

Simulation Steps

1. Download “Yet Another Bacnet Explorer-Yabe” from Yabe
2. Open “Bacnet.Room.Simulator” that is installed with Yabe (Yabe\AddOn folder)
   • 
   • Noticte that BACnet device ID will change if multiple instance of the application is opened
3. Add devices in Yabe OVER UDp
   • 
   • Simulated device IP will show up when you hover the mouse
     • 
4. Find the Object Instance on the top right corner
   • Object Instance is “0” as set point
     • 
5. Set the following information on LabVIEW B.IP Test Read from “C:\Program Files (x86)\National Instruments\LabVIEW 2021\examples\Endigit\Endigit BACnet API”
   • Set Local IP
   • Set Remote IP (same on the same PC)
   • Object Instance to “0”
   • Object Type “Analog Value”
   • Property “Present Value”

   • Click “Run” and you will see “70” on the Value indicator

     •