A BACnet Object Identifier value shall consist of two components:

(1) A 10-bit object type, representing the BACnetObjectType of the object, with bit 9 the most significant bit and bit 0 the least significant.

(2) A 22-bit object instance number, with bit 21 the most significant bit and bit 0 the least significant.

Bit Number: 31 22 21 0

|---|---|---|---|---|---|---|---|

| Object Type |Instance Number|

|---|---|---|---|---|---|---|---|

Field Width: <----- 10 ----> <---- 22 ----->

The encoding of an object identifier value shall be primitive, with four contents octets as follows:

Bits 9 through 2 of the object type shall be encoded in bits 7 through 0 of the first contents octet. Bits 1 through 0 of the object type shall be encoded in bits 7 through 6 of the second contents octet. Bits 21 through 16 of the object instance shall be encoded in bits 5 through 0 of the second contents octet. Bits 15 through 8 of the object instance shall be encoded in bits 7 through 0 of the third contents octet. Bits 7 through 0 of the object instance shall be encoded in bits 7 through 0 of the fourth contents octet.

Example: Application-tagged object identifier value

ASN.1 = ObjectIdentifier

Value = (Binary Input, 15)

Application Tag = ObjectIdentifier (Tag Number = 12)

Encoded Tag = X'C4'

Encoded Data = X'00C0000F'

The BACnetObjectIdentifier is a simple DataType and subtype of 0:UInt32. Its representation in the AddressSpace is defined in Table 92.

Table 92 – BACnetObjectIdentifier Definition

Attribute		Value
BrowseName		BACnetObjectIdentifier
IsAbstract		False
References	NodeClass		BrowseName	DataType	TypeDefinition	Other
Subtype of 0:UInt32