Bytes Assignment For Data Exchange P - GE Profibus - DP Bus Instructions Manual

Profibus-DP Bus
3. BYTES ASSIGNMENT FOR DATA EXCHANGE
The Profibus-DP interface card uses a 16-byte frame. The first 8 bytes represent the configuration channel for
the non-cyclic data exchange, the other 8 are the process data channel for the cyclic exchange.
The bytes assignment is as follows:
_\
I
Configuration channel
I
Process data channel
P I
1 2 3 4 5 6 7 8 WORD0 WORD1 WORD2 WORD3
Data/Error
Subindex/Type/Word PDC
Index
Control byte
As to the Data/Error and Index fields, the data format is arranged from the least to the most significant byte. The
meaning of the fields is the following:
A ) Data frame from Master to Slave:
1 ) Data / Error.
The content of this field depends on the kind of service carried out: in case of writing it
contains the parameter value, in case of reading it has no meaning.
2 ) Subindex/Type/Word PDC.
3 ) Index.
4 ) Control byte.
It contains the parameter subindex, if any. If the parameter has no subindexes it has to
be set to 0. For parameters faith subindex, this has to be set from 1 to the max. number
of parameter elements; the value 0 is not accepted and rejected. It is not possible to read
the whole object, but only its single elements. In case of service carried out towards the
DGFC option, this field shquld contain the data type. In case of Process Data Channel
configuration (see chapter 4), this field contains the number of the PDC Word involved
in the operation. In case of virtual digital input/output configuration (see chapter S),
this field contains the number of the digital channel involved in the operation .
Index of the parameter involved in the operation with format low byte - high byte.
The meaning of this byte is'described in 3.1.
BYTE ASSIGNMENT FOR DATA EXCHANGE