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II - DCE FEL ČVUT v Praze

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Structure of<br />

command data<br />

record<br />

Notes on<br />

command<br />

Notes on response<br />

I/O Modules with Intrinsically-Safe Signals<br />

C79000-G7076-C152-04<br />

The following figure shows the structure of data record +0, which you can<br />

use to write a command in the transfer area of a client. The HART analog<br />

module transmits the command to the connected HART field device.<br />

Byte 0<br />

Byte 1<br />

Byte 2<br />

Byte 3<br />

to<br />

Byte 239<br />

7 6 5 4 3 2 1 0<br />

0 0<br />

always 0 (“monodrop,” 1 field device per channel)<br />

1=inseparable command sequence<br />

1=module command<br />

0=HART command<br />

Command number<br />

Number of bytes for command (can<br />

be taken from the HART command<br />

syntax)<br />

.<br />

.<br />

.<br />

Command data<br />

according to HART<br />

specification<br />

Length: No. of bytes<br />

max. 237 bytes<br />

Fig. 4-14 Command data record of the HART analog module<br />

SIMATIC S7 HART Analog Modules<br />

The same client must not send a second command until the response to any<br />

previous command has been read. If you want to prevent commands from<br />

another client being processed in between, you must set the bit “inseparable<br />

command sequence” in your command:<br />

The inseparable command sequence is maintained as long as the bit<br />

“inseparable command sequence” is set.<br />

The inseparable command sequence is terminated if the bit “inseparable<br />

command sequence” is not set, or automatically after 10 seconds by the<br />

module.<br />

While an inseparable command sequence is set for one client, one<br />

command from each of the other clients can be stored temporarily in the<br />

buffer. The stored commands are processed once the inseparable<br />

command sequence has been terminated.<br />

To read the response data record you must make sure that an up-to-date<br />

response data record has arrived:<br />

If the processing state in the response data record indicates “successful”<br />

or “error,” the data record contains current response data or error<br />

messages respectively.<br />

Alternatively you can evaluate the “data ready” in the user data area: the<br />

transfer area of each client is allocated a bit in the user data area which is<br />

set when new data arrrive (see Figure 4-20).<br />

4-31

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