BACnet communications overview

Communications via BACnet MS/TP protocol is available on iEM3465 / iEM3565 meter models.

The information in this section is intended for users with an advanced understanding of BACnet protocol, their communications network and their power system.

Key terms

Term	Definition
APDU	Application protocol data unit, that data portion of a BACnet message.
Confirmed message	A message for which the device expects an answer.
COV	Change of value, sets the amount by which a value has to change in order for the meter to send a subscription notification.
Device	A BACnet device is a unit that is designed to understand and use BACnet protocol (for example, a BACnet-enabled meter or software program). It contains information about the device and device data in objects and object properties. Your meter is a BACnet device.
MS/TP	Master-slave/token-passing over RS-485.
Object	Represents the device and device data. Each object has a type (for example, analog input or binary input) and has a number of properties.
Present value	The current value of an object.
Property	The smallest piece of information in BACnet communications, it consists of a name, data type and value.
Service	Messages from one BACnet device to another.
Subscription	Creates a relationship between the server and the meter, so that when the present value property of an object changes by more than the configured COV threshold (COV_Increment), a notification is sent.
Subscription notification	The message the meter sends to indicate a COV event has occurred.
Unconfirmed message	A message for which the device does not expect an answer.