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Re: HART 6.0 vs 7.0

Message posted by Romilly ( : on 16 May 2009 at 11:40:16.

in reply to: HART 6.0 vs 7.0 posted by Charlie Sannes on 14 May 2009 at 15:03:23.

Yes, absolutely! The HART revision rules are very strict about this, back to rev. 5.

The way this usually works is that a master or slave device must ignore anything it doesn't understand, without complaining. Commands may be added, never removed: a slave may respond Command Not Implemented. Within a command, data may be extended, never changed or reduced: a master or slave just ignores extra data bytes beyond what it expects.

There are a few special cases, for example dealing with 16-bit extended command numbers, where the response to a command depends on the revision level of the master. Handling for these is explicitly specified in the HART 7 command specs: the slave must detect this from the command data, and respond as though it was a rev. 6 device.

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