Rockwell Automation 1794-OF8IH FLEX Isolated Input/Output HART Analog Modules - Manual (Page 130)

Publication 1794-UM065B-EN-E - September 2010
118 FLEX I/O HART Modules Network Messaging
To protect against a second HART host communicating to modules, the
HART_lock bit is set in the Group for Group assembly.
• Cold Start
Cold Start indicates that the HART I/O module has made a cold start
and the bit is reset when it was first read.
HART Frame Enhancements Attribute 69 hex for Host Access Group 1 contains only six bytes. Since every
HART response starts with these six status bytes, this attribute only contains
this information. In addition, you need to account for these six status bytes
when selecting the associated response Attribute. Add six bytes to the size of
the HART response to accommodate the status bytes.
If you do not know the size of the expected response from the HART module,
read Attribute 69 hex for Host Access Group 1. The returned data indicates
which Assembly Index contains the response. Once you get this index, issue a
MSG or CIO to the associated Attribute. For example, if the Assembly Index
is 14, issue a MSG or CIO to Attribute 6D hex.
The Response Error field indicates if the response is available. Once a HART
command is issued, it takes a small amount of time to send the message via
HART protocol to the field devices, time for the field device to interpret the
command, and time to send the response back to the FLEX I/O HART
module. During this time, you could request the response prior to the module
obtaining it from the field device. In this case, a Response Not Available
response is returned in the Response Error field. The module assumes another
request will gather the response.
Value Meaning
0 Not locked
1 Locked