Rockwell Automation 1770-HT8 SMART TRANSMITTER - Manual (Page 77)

Communicating with the Smart
Transmitter Interface
Chapter 4
Communicating with the Smart Transmitter
Interface
4-12
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 as shown in Table 4.C. If the last message was received without
error, the field device will clear bit 7 and return a device dependent
response code in the other seven bits.
The second byte of this response code returns the operating status of
HART field devices as indicated in Table 4.D. 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 should ignore any values in the data field
when a communications error is detected.
Table 4.C
HART Protocol Ć Communication Error Code
Bit Error Code Description
7 Communications Error If set, the field device has detected a communications
error. Bits 0 Ć 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 overĆwritten 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 at this time.