in reply to: HART Slave Response on error posted by Girish on 24 January 2011 at 10:16:24.
What to do, when a field device detects a communication error, depends on where in the command message the error is found. See Section 5.4 and Table 1 in the Token-passing Data Link Layer spec HCF_SPEC-81 (Revision 8.2).
In the non-fatal cases, when the field device replies, it sends the two Status bytes as usual: the first byte indicates the nature of the communication error detected (for example Bit 6 for a parity error), and the second byte is all zeros. No further data is sent.
A field device always sends the Byte Count byte, before the two Status bytes. And the Byte Count always includes the two Status bytes as well as the real data bytes. So the Byte Count in such a case is just 2, and the two Status bytes are immediately followed by the Checksum byte.