II - DCE FEL ČVUT v Praze

Structure of
command data
record
Notes on
command
Notes on response
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
The following figure shows the structure of data record +0, which you can
use to write a command in the transfer area of a client. The HART analog
module transmits the command to the connected HART field device.
Byte 0
Byte 1
Byte 2
Byte 3
to
Byte 239
7 6 5 4 3 2 1 0
0 0
always 0 (“monodrop,” 1 field device per channel)
1=inseparable command sequence
1=module command
0=HART command
Command number
Number of bytes for command (can
be taken from the HART command
syntax)
.
.
.
Command data
according to HART
specification
Length: No. of bytes
max. 237 bytes
Fig. 4-14 Command data record of the HART analog module
SIMATIC S7 HART Analog Modules
The same client must not send a second command until the response to any
previous command has been read. If you want to prevent commands from
another client being processed in between, you must set the bit “inseparable
command sequence” in your command:
The inseparable command sequence is maintained as long as the bit
“inseparable command sequence” is set.
The inseparable command sequence is terminated if the bit “inseparable
command sequence” is not set, or automatically after 10 seconds by the
module.
While an inseparable command sequence is set for one client, one
command from each of the other clients can be stored temporarily in the
buffer. The stored commands are processed once the inseparable
command sequence has been terminated.
To read the response data record you must make sure that an up-to-date
response data record has arrived:
If the processing state in the response data record indicates “successful”
or “error,” the data record contains current response data or error
messages respectively.
Alternatively you can evaluate the “data ready” in the user data area: the
transfer area of each client is allocated a bit in the user data area which is
set when new data arrrive (see Figure 4-20).
4-31