BACnet

BACnet is the standard protocol of building automation: air handling units, fan coils, heat pumps, lighting and fire panels. inSCADA supports BACnet/IP natively — no separate gateway application is involved.

Protocol value	Role
BACnet	Client — reads and writes field devices
BACnet/IP Server	Server — publishes inSCADA’s own values as a BACnet device

Core concepts

Objects and properties

A BACnet device is made of objects. Each has a type (analog input, binary output, multi-state value, …) and an instance number; together those address the object uniquely within that device.

An object has several properties. The one read and written is almost always Present_Value — property identifier 85.

Instance numbers

Both device and object instance numbers are 22-bit: 0 – 4194303. On the device side 4194303 means “unassigned”, so a device instance goes up to 4194302.

The object type is not a list

The object type is a 10-bit number (0 – 1023). Values above 127 are vendor-specific and legitimate, which is why it is entered as a number rather than picked from a fixed list.

COV — notify on change

Rather than polling a value, BACnet can notify when it changes: COV (Change of Value). On a point that rarely moves, that cuts both network traffic and device load noticeably.

Write priority

A BACnet output is written at a priority from 1 to 16, and the highest-priority write wins. 1 is the highest, 16 the lowest.

The default priority is the lowest

inSCADA writes at 16 by default. That means higher priorities — manual overrides, fire scenarios — override what inSCADA writes, which is what most installations want. The commonest cause of “I wrote it and nothing changed” is a higher-priority write still standing on the point.

Addressing

A BACnet address is not a byte offset, so start address is not used.

Discovering devices

inSCADA can browse the BACnet devices and objects on the network, so while defining a variable you pick the object type and instance from a list instead of typing them.

Sub-pages

• BACnet Client — reading and writing field devices
• BACnet/IP Server — publishing your own values