Because CAN and HART have different physical interfaces, an RS-232 converter needs to be added between the radios and the CAN/HART device for proper operation.
Modbus, CAN, HART & Industrial protocols
If you are working with industrial automation equipment, chances are you have run across control or monitoring equipment that uses Modbus, CAN, HART or other industrial protocols. Digi has created a family of stand-alone radio modems that interface to RS-232 and RS-485 serial devices. Since the radios can interface to both a two wire and four wire RS-485 system and are transparent to the data format, generally they can run most industrial protocols as long as the timing requirements are not too strict. The radios add some additional delay that traditional wiring does not have, but since the radios will transparently pass any incoming data, most protocols will operate without any additional hardware or software adjustments.