No new HART 5 devices will be registered after March 31, 2011.
Please develop HART 6 or HART 7 conformant products for the best interoperability experience. You can find the HART 5~7 comparisions here.
HART protocols are backward and forward compatible, that means a HART 5 host (handheld/communicator, gateway, asset management system...) can communicate with a HART 6 or 7 device and vice versa:
If a HART 5 host is communicating with a HART 6 or 7 device, the host can only identify the informations defined in HART 5 specs, such as HART revision number, Unique ID, dynamical variables (PV, SV...), tag, range values...New features defined in HART 6 or 7, such as device variables classifications, long tag, etc., cannot be recognized by HART 5 host;
If a HART 7 host is communicating with a HART 5 device, the host can identify all the informations in this HART 5 device since there is no HART 5 features lossing in HART 6 & 7 revisions.