WAGO I/O SYSTEM 750 XTR
Diagnostics 121
750-333/040-000 FC PROFIBUS G2 12MBd XTR
Manual
Version 1.4.0
9.4
Acyclic Communication according to DP/V1
In addition to cyclic data communication (PROFIBUS DP standard in compliance
with IEC 61158), PROFIBUS DP also offers acyclic communication services as
an option. These acyclic services can be performed parallel to cyclic data
transfer. In process engineering applications, the optional services allow
industrial devices to be operated using PROFIBUS DP. Standard field devices
and devices that require these optional extensions can be operated on the same
bus. The data blocks are addressed via the slot number and the data block
number (index) of the module. The meaning of the slots and indices can be set
according to the device specifications. This way, the user can either access the
data or the parameter sets within a field device. To distinguish between a
standard DP and an acyclic DP/V1 device, some keywords have been added to
the GSD file.
Acyclic communication is no longer possible once cyclic data exchange has been
interrupted. In the parameter assignment message, the Class 1 master activates
the acyclic communication service of the device. In the Data_Exchange, the
Class 1 Master that parameterized and configured a slave can use the acyclic
service of the slave. Acyclic communication is no longer possible when exiting
cyclic data communication.
For the extended services, a distinction is made between Master Class 1 / Slave
Functions (MSAC1) and Master Class 2 / Slave Functions (MSAC2).
The use of an MSAC2 connection requires prior establishment (initiate) and
subsequent suspension (abort) of the communication channel. Among other
things, this action serves to monitor the MSAC2 connection. An MSAC1
connection is monitored by the always required MSCY0 connection.
The bus coupler/controller supports the following acyclic services according to
IEC61158-3:
Table 71: MSAC1 Service
MSAC1 service
Requester Responde
r
MSAC1_Read
X
MSAC1_Write
X
Table 72: MSAC2 Service
MSAC2 service
Requester Responde
r
MSAC2_Initiate
X
MSAC2_Abort
X
X
MSAC2_Read
X
MSAC2_Write
X
The MSAC1 services can be used when the DP/V1 operation has been activated
in the parameter data and the cyclic MSCY0 connection is established. The