How many BACnet objects can be defined per CPU?

FAQ #101118

 

As a rule of thumb it a PCD2.M5xx0 or a PCD3 CPU (with FW 1.10.xx or later) can handle up to 1200 BACnet objects. This applies if the 800/1200 BACnet objects consists of a mix of different BACnet objects.

Please note that in case a PCD2.M5xx0 or a PCD3 CPU does handle between 800 and 1200 BACnet objects then it is to be verified carefully whether the CPU is still able to treat the other tasks of the application (the cyclic treatment of application program and/or non-BACnet communication tasks) in every situation.

In case the CPU has less than 800 BACnet objects to treat the CPU performance is usually sufficient to treat the user program and other communication tasks.

Why is it that difficult to define the maximal amount of BACnet objects per CPU?
The BACnet related tasks to be executed by the CPU vary heavily depending on the BACnet object and the features configured for this object. A Binary Input (BI) without intrinsic alarming does not generate a lot of CPU load compared to an Analogue Value (AV) with intrinsic Alarming enabled. Additionally the required memory of e.g. a Calendar object or a Trendlog object is far higher than for binary/analogue values or inputs.