WEG DeviceNet CFW500 User Manual - page 24
Communication between class 2 master and slave (MS2):
Initiates the connection (Initiate)
Data acyclic reading (DS_Read)
Data acyclic writing (DS_Write)
Aborts the connection (Abort)
DP-V1 requests use an SD2 type Profibus DP telegram – with variable data length. This type of telegram has the
following fields:
Telegram Header
Data Unit
Telegram End
SD
LE
LEr
SD
DA
SA
FC
DSAP
SSAP
DU
FCS
ED
68h
xx
Xx
68h
xx
xx
xx
xx
xx
xx ...
xx
16h
SD
Telegram start delimiter (Start Delimiter)
LE
Telegram length, from the DA field to the DU (Length)
LEr
Telegram length repetition (Length repeat)
DA
Destination Address
SA
Source Address
FC
Function Code
DSAP Destination Service Access Point
SSAP Source Service Access Point
DU
Data unit, size 1 to 244 (Data Unit for DP services)
FCS
Telegram checking byte (Frame Checking Sequence)
ED
Telegram end delimiter (End Delimiter)
In this telegram it matters to describe the data structure in the DU field, where the form to access the drive
parameters is defined. The other fields follow the defined by the Profibus specification and, normally, are
controlled by the network master.
5.2.2 Data Addressing
In the functions for reading and writing via acyclic data, these data are addressed with a numbering indicating
which slot and index are being accessed. The slots can be used to address different physical segments of an
equipment (a modular equipment for instance) or even logical segments inside a single equipment. The index
indicates which data inside the segment is being accessed.
Profibus Network
↔
Slave
Slot 0
Slot 1
...
Slot N
...
Index 0
Index 0
Index 0
Index 1
Index 1
Index 1
Index 2
Index 2
Index 2
...
...
...
Index 254
Index 254
Index 254
Figure 5.1: Acyclic Data Addressing
5.2.3 Reading/Writing DP-V1 Telegrams
In the Profibus DP protocol, the writing (DS_Write) and reading (DS_Read) DP-V1 telegrams used to access the
parameters have the following structure:
Writing Telegram (DS_Write):
Request
(master -> slave)
Header
Data Unit (DU)
End
Function
5Fh
Slot
0
Index
47
Size
n
Request
Data
(n bytes)
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