ABB Advant AC500 Manual page 48

DP-V1 offers reading and writing single parameters.
The possibility to read single parameters is an important advantage: If e.g. during commissioning the
"Set current" for a motor is modified locally by the electrician, then the control system must be able to
read this value to back it up into its data base.
The PDP22 (PROFIBUS DP-V1) also allows to suppress the block parameter transfer. This avoids that
the parameters are overwritten during power-up of the slave / device.
The appropriate parameter is evaluated in the PDP21 / PDP22 and is not sent to the device and cannot
be set via the device.
The appropriate parameter is "Ignore V0 Parameters" or "Use V0 Parameters" respectively and is
available in the .GSD file for DP-V1.
In former times a separate master class 2 was needed to read and write single parameters. Currently,
most of the control systems offer a class 1 master capable to perform acyclic DP-V1 services to read
and write all data types.
Note: In all cases only the bus master can start the data exchange on the PROFIBUS DP bus.
PROFIBUS DP Master Class 1, PROFIBUS DP Master class 2
CPU
Slave
PROFIBUS DP Master Class 1
(usually a control system / station):
- continuous cyclic data transfer to
all (or selected) slaves
transfer of other basic data
- write and read bus specific data
(baud rate, time-out,....)
- write configuration data
- write block parameters
- read diagnosis data
Some Master Class 1 are able to
- read and write single parameters
(acyclic data transfer)
Figure: PROFIBUS DP Master, class 1 and class 2
____________________________________________________________________________________________________________
V2
AC500 Hardware
PROFIBUS
DP Master
Class 1
Control System
Slave
PROFIBUS
DP Master
Class 2
Slave Slave
PROFIBUS DP Master Class 2
(usually an operator station / PC)
- gets access to one slave after
request (initiate) for a limited time,
- reads and writes acyclic data
Some Master Class 2 are able to
- read cyclic data
1-48 System data
Slave
AC500 / Issued: 05.2007