Balluff BTL5-T110 Technische Beschreibung Seite 68

BTL5-T110...
Configuration and Profibus Connection –
Transducer Class 3/4
6 Startup (cont.)
6.3.2 Acyclic communication
between a Class 1 master
and a slave (MSAC_C1)
To send the data the FDL service
SRD is used with SAP 51. The
master parameterizes and
configures the slave as in cyclic
data communication. Then it can
carry out the previously described
acyclic services with the slave.
The process for such acyclic com-
munication can be seen in Fig. 6-7.
Communication is initiated with a
call-up telegram (Write.req). The
telegram describes what is to be
done, e.g. read or write a
parameter. Processing of this
request then begins in the slave. If
a response to this request is not
immediately available, several poll
cycles occur until internal
processing has been completed.
The result is picked up in the
response telegram (Read.req).
Byte 0 Byte 1 Byte 2
SD LE LEr
68h X X
Table 6-2: Message structure of Write.req
6.3.2.1 Description of the telegram
Write.req
Write.req is used to establish a
connection and inform the slave of
the action to be performed.
When opening the connection the
master starts an internal timer for
communication monitoring. Several
polling cycles can elapse until the
slave provides the requested data.
If the slave does not reply within
the set time, the communications
connection (also for cyclic data
communication) is aborted. After a
connection abort the slave must be
re-parameterized and re-
configured. If the slave replies with
an error message, the Class 1
master attempts the request again.
Byte 3 Byte 4 Byte 5
SD DA SA
68h 8h 8h
Byte 6 Byte 7 Byte 8
FC DSAP SSAP
X 33h 33h
Byte 9..n-2 Byte n-1 Byte n
DU FCS ED
see
Tab. 6-3:
Structure X 16h
of the DU
in Write.req
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