Allen-Bradley 857-VPA3CG, User Manual, Page: 2 / 14

2 Rockwell Automation Publication 857-UM003B-EN-P - December 2017
857-VPA3CG Profibus DP Option Module
PROFIBUS-DP Optimized for high speed and inexpensive hook-up, this PROFIBUS version is
designed especially for communication between automation control systems and
distributed I/O at the device level.
PROFIBUS-DP can be used to replace parallel signal transmission with 24V or
0...20 mA.
PROFIBUS-PA PROFIBUS-PA is designed especially for process automation. It permits sensors
and actuators to be connected to one common bus line even in intrinsically safe
areas. PROFIBUS-PA permits data communication and power over the bus using
2-wire technology according to the international standard IEC 1158-2.
PROFIBUS-FMS PROFIBUS-FMS is the general-purpose solution for communication tasks at the
cell level. Powerful FMS services open up a wide range of applications and
provide great flexibility. PROFIBUS-FMS can also be used for extensive and
complex communication tasks.
PROFIBUS specifies the technical and functional characteristics of a serial
fieldbus system with which decentralized digital controllers can be networked
together from the field level to the cell level. PROFIBUS distinguishes between
master devices and slave devices.
Master devices determine the data communication on the bus. A master can send
messages without an external request when it holds the bus access rights (the
token). Masters are also called active stations in the PROFIBUS protocol.
Slave devices are peripheral devices. Typical slave devices include input/output
devices, valves, drives, and measuring transmitters. They do not have bus access
rights and they can only acknowledge received messages or send messages to the
master when requested to do so. Slaves are also called passive stations.
PROFIBUS-DP Device Profiles This section outlines the different PROFIBUS-DP device profiles.
Continuous Mode with Fixed Data Set
In this mode, the 857 protection relay is sending a configured set of parameters
continuously to the PROFIBUS-DP master.
Calculation of the PROFIBUS-DP Buffer Length
The needed buffer length for PROFIBUS-DP data transfer depends on the
biggest offset of any activated parameter and the size of this parameter. The offset
and the activation for each available parameter are configurable.