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Peripheral Devices
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8.12.2.1 Using the extended format
The Extended format gives you an alternative method of specifying the targeted type of process data.
When using this method you specify what to read or write to using an address instead of the bits d2..d0 in
the command word. The address is the same as used for the Serial Communication (see its sub chapter:
Accesses from External communication device).
An advantage of using this method is that you in addition of accessing the traditional process data, i.e.
cycle data, trace, and events, also can read and write to the PLC input/output area normally used for the
External communication devices and the API.
The address is specified in the first word of the Process data, i.e. the word following next after the
command word. I.e. Process data should be laid out as below:
Process Data
0 Target Addr (MSB)
1 Target Addr (LSB)
2
3 Message
Data
: (m bytes)
m + 1
The layout of Message Data depends on whether the targeted data is of type "Process Data" (i.e. Cycle
Data, Event Data, Trace Data and Setup Data) or "PLC Data".
Message Data
to/from the PLC
0 LEN (MSB)
1 LEN (LSB)
2 Data byte 1
3 Data byte 2
:
n + 1 Data byte n
Message Data as
Process Data
0 SEQ (MSB)
1 SEQ (LSB)
2 LEN (MSB)
3 LEN (LSB)
4 Data byte 1
5 Data byte 2
:
n + 3 Data byte n
LEN
LEN
The format of Process Data is the very same as used the External communication devices, but the format
of PLC Data is slightly different. For the fieldbus device the first word of the Message Data specifies the
length of data to be read or written. If writing, this is then followed with as many bytes of PLC data that is
specified.
Also, note that if the extended format is used for the command then the target address of the command
will be included in the response as well.