Spectrum Controls 1756sc-OF8H Series A - Manual (Page 159)

Appendix D: HART Protocol Overview 145
Generally, burst mode is only useful if there is just one field device
attached to a pair of wires (since only one field device on a loop can be in
burst mode at any one time). In burst mode, more than three messages
can be transmitted per second.
Status Status Status Status Status
Two bytes of status, also known as the response code, are included in
every message from a field (slave) device. These two bytes convey three
different types of information: communication errors, command responses,
and field device status.
If an error is detected in the outgoing communication, the most-significant
bit (bit 7) of the first byte is set to 1, and the details of the error are
reported in the rest of that byte; the second byte is then all zeros.
If no error is detected in the outgoing communication, bit 7 of the first byte
is 0, the remainder of the byte contains the command response, indicating
any problem with the received command, and the second byte contains the
field device status, indicating the operational state of the slave device.
Communication errors are mostly those that would be detected by a
HART: parity, overrun and framing errors. The field device also reports
overflow of its receive buffer, and any discrepancy between the message
content and the checksum received.
Command response codes (integers in the range 0 to 127) are categorized
as either errors or warnings, and as having either a single meaning or
multiple meanings