User manual

Publication 1794-UM063A-EN-P - March 2006
Additional HART Protocol Information C-5
Response Code
This two-byte code contains the HART field device status as sent by that
device. Field devices detecting a communications error set the most significant
bit, bit 7, of the first byte and identify the error in the other seven bits. If the
last message was received without error, the field device will clear bit 7 and
return a device-dependent response in the other seven bits.
The second byte of this response code returns the operating status of HART
field devices. This byte may default to 0 when a communications error occurs
as indicated by bit 7 of the first byte being set.
IMPORTANT
The host processor ignores any values in the data field
when a communications error is detected.
Table C.3 HART Protocol — Communication Error Code
Bit Error Code Description
7 Communications Error If set, the field device has detected a
communications error. Bits 0…6 indicate the
type of error.
6 Vertical Parity Error The parity of one or more of the bytes received
by the HART field device is incorrect.
5 Overrun Error At least one byte of data in the receive buffer of
the HART field device was over-written before it
was read.
4 Framing Error The stop bit of one or more bytes received by the
HART field device was not detected.
3 Longitudinal Parity Error The longitudinal parity calculated by the HART
field device does not match the longitudinal
parity byte at the end of the packet.
2 Reserved Set to 0.
1 Buffer Overflow The packet is too long for the receive buffer of
the HART field device.
0 Undefined Not defined.