scope:

ClimateTalk is an open standard that defines a set of messages and commands to enable interoperability, enhanced user interface, and machine to machine control independent of the physical layer connecting the devices.

The messages and commands defined by ClimateTalk Information Model (CIM) are the presentation and application layers as defined by the OSI Model.¹ ClimateTalk Applications are fully defined at Layer 7 of the OSI model by a combination of a Device Specific Application Profile, the Generic Application Specification, and the Command Reference.

ClimateTalk messages can be carried over any physical medium following the OSI model. The ClimateTalk Presentation Layer defines how messages are executed over the various physical mediums in use.

CT-485 and CT-LWP are wired serial physical and network layers designed to support the formation of ClimateTalk networks and transport ClimateTalk messages, but other OSI-based protocols-including wireless transports-can be used as well.

CT-485 is a Physical, Data Link, and Networking set of specifications that define one of the physical media over which ClimateTalk messages are sent. CT-485 is a variant of EIA/TIA-485 standards with provisions against incorrect wiring and grounding requirements that meet the needs of residential systems.

This document defines the Data Link Layer requirements for CT-485. Corresponding to OSI Layer 2, the Data Link specification defines CRCs, bit level error correction, physical node addressing, subnet addressing, and data transmission rules. See Figure 1 for a diagram of relevant standards.

The ClimateTalk Open Standards package shown in Figure 1 prescribes the requirements to ensure proper network formation of interoperable devices. Each device must comply with the mandatory requirements defined in this document as well as all other ClimateTalk standards applicable to the device functionality.

Membership in the ClimateTalk Alliance as well as successful completion of conformance testing is required for listing a product as a ClimateTalk Certified Device.