Hart Communication Interface - Siemens SIMATIC ET 200SP Manual

HART function

4.3 HART communication interface

4.3 HART communication interface
Data records
The HART commands are sent over data records to the connected field device as "external
HART jobs" from the client (e.g. PDM or the STEP 7 user program). The response of the field
device is made available again in the system via data records.
HART communication may only be handled by one client (e.g., PDM) per channel. If a channel
is handled by several clients, the response made available by the module cannot be allocated
to one client with certainty. The analog module AQ 4xI HART does not support client
management.
Each client/channel is allocated fixed data records:
Table 4-6
Channel
0
1
2
3
The corresponding data records are transferred to the module with the "WRREC" instruction
and read by the module with the "RDREC" instruction.
Errors during the transfer are indicated at output parameter STATUS.
Errors during interpretation of the request data record are signaled in the corresponding
response data record. The faulty request can be read back again using the request data record.
Rules
● After having written a request data record, a client must read the response data record
before it may write another request data record.
● The client can evaluate the "processing status" in the response data record: If the
"processing status" indicates "successful" or "error," the response data record contains
current response data or error displays.
● The response data record must always be read completely because the analog module may
modify the data record after the initial reading with "successful" or "error" status.
If the processing status in the response data record indicates "successful" or "error", the
data record contains current response data or error displays.
● The client may only write a request data record to the module again when it has read the
response to the previously written request data record via the corresponding response data
record.
If this condition is not fulfilled, the response from the module is overwritten.
● The STATUS component in the response frame (HART device status in the response data)
provides information on whether errors have occurred and, if so, which errors.
22
Structure of the data records
Request to the field device
80
82
84
86
Data record number
Response from the field device
81
83
85
87
Analog Output Module AQ 4xI HART HF
Manual, 05/2019, A5E35098013-AA