Before any multi-vendor BACnet integration in a project, read the vendor device's PICS (Protocol Implementation Conformance Statement) to verify exactly: profile (B-OWS / B-BC / B-ASC...), supported services, supported object types and writable properties.

A PICS is effectively the BACnet user manual of a device. It follows the standardised format defined in ASHRAE 135 Annex L, listing the exact services supported (which can differ from the standard's full set), the object types implemented, which properties are writable versus read-only, and any vendor-specific notes. Skipping the PICS is a fast track to unpleasant surprises at integration time: a property assumed writable that turns out to be read-only, COV that is not supported, or a Schedule object with restricted features. PICS files are available on vendor websites and from the btl.org Product Listing.

Archive the PICS PDF used during design alongside the as-built drawings; the same model can change behaviour across firmware revisions, and you will want to know which document the design was based on.