Understanding the PICS document

A PICS (Protocol Implementation Conformance Statement) is the "BACnet data sheet". This document describes the scope of the BACnet device implementation.

The PICS document for Beckhoff controllers can be downloaded here: https://download.beckhoff.com/download/Document/certificates/beckhoff_bacnet_ip_pics_en_rev14_ver4.0.pdf

The PICS describes the supported object types and for each object type, which properties are supported, the read or write access (so-called conformance code) and possible property limitations.

In addition, the supported Data Link Layer, character sets, segmentation support, etc. is described as well.

The third element of the PICS document is the list of supported BIBBs (BACnet Interoperability Building Blocks). The standard describes A-side and B-side BIBBs.
A-side BIBBs are those issued by a client requesting something from or to a B-side device (server).

To use a specific functionality, such as Change-of-Value, both sides, client and server, must support the corresponding BIBB.

Example:

DS-COV-A: Client requests data using the subscribed Change-of-Value.

DS-COV-B: The server responds to COV subscriptions from the client and provides the data to the client when the value has changed by sending a COV notification.