Types Of Acyclic Communication; Acyclic Communication Via The Class 1 Master; Acyclic Communication Via The Class 2 Master - GE VersaPoint IC220PBI002 User Manual

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Types of Acyclic Communication

Acyclic Communication Via the Class 1 Master

The Class 1 master carries out parameterization during slave startup. It is also the
master for cyclic data traffic.
The Class 1 master can also control an RS-232 interface acyclically, or read a
parameter from the RS-232 device.
Corresponding read and write accesses are defined for the Class 1 master.
Because it already has a connection to the slave during cyclic data traffic, the
Class 1 master does not have to establish an explicit connection (using "Initiate"),
but can communicate with the slave directly via "Read" and "Write".
Before programming the application, check whether the control system or
configuration tool supports DP/V1. If not, you can use the functions offered by the
cyclic process data channel (DP/V0).

Acyclic Communication Via the Class 2 Master

For communication in the Class 2 master, the data fields are identical to those of
Class 1 communication. For Class 2, only the Service Access Points (SAP) are
different. Class 2 requires the use of "Initiate" and "Abort" to establish and release
the connection via SAP49 and 50. If DP/V1 devices are already in use, the
routines for connection management can be adapted easily.
The Class 2 master can be implemented in various forms, such as a display
device or operator interface. In a display device, the data is fetched from the slave
on request if, for example, a specific parameter is to be read. Access to the
operator interface is usually acyclic.
Only one active DP/V1 communication is permitted at any time. It is possible to
connect a total of up to eight PCP-compatible modules to the Profibus DP/V1NIU.
8-2 VersaPoint™ I/O System Profibus-DP NIU User's Manual – August 2005 GFK-1911B