Device Types; Bus Access Protocol - Omron WS02-9094G - V1.0 Operation Manual

Overview of PROFIBUS
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Device Types

Master Devices
Class 1 Master (DPM1)
Class 2 Master (DPM2)
Slave Devices
Device Profile
PROFIBUS DP-V1
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Bus Access Protocol

OSI Layer 2: Bus Access
Protocol
Medium Access Control
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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, as long as it holds the bus
access right (the token). Masters are also referred to as active devices in the
PROFIBUS standard.
There are two types of master devices:
A PROFIBUS DP Class 1 Master (DPM1) device is a central controller, which
exchanges information with the decentralized devices (i.e. DP slaves) within a
specified message cycle.
PROFIBUS DP class 2 Master (DPM2) devices are programmers, configura-
tion devices or operator panels. They are used during commissioning, for con-
figuration of the DP system, or for operation and monitoring purposes.
The CS1W-PRM21 and the CJ1W-PRM21 are both PROFIBUS DP Class 1
Master devices.
Slave devices are peripheral devices. Typical slave devices include input/out-
put 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. Slave devices are also
called passive devices
To enable the exchange of devices from different vendors, the user data has
to have the same format. The PROFIBUS DP protocol does not define the for-
mat of user data, it is only responsible for the transmission of this data. The
format of user data may be defined in so called profiles. Profiles can reduce
engineering costs since the meaning of application-related parameters is
specified precisely. Profiles have been defined for specific areas like drive
technology, encoders, and for sensors / actuators.
PROFIBUS DP-V1 is an extension to the PROFIBUS DP protocol standard. It
defines acyclic message services between a PROFIBUS DP-V1 Master and a
PROFIBUS DP-V1 slave device. These acyclic message services allow
exchange of extended parameter settings as well as extended diagnostics
and alarm information, during regular I/O data exchange. PROFIBUS DP-V1
devices must at least support PROFIBUS DP.
PROFIBUS DP-V1 services are designated as MSACn services (Master-
Slave Acyclic, Class n), in which n designates the Master Class (i.e. 1 or 2).
The CS1W-PRM21 and the CJ1W-PRM21 both support PROFIBUS DP-V1
Class 1 Master functions as of Unit version 2.0.
The PROFIBUS bus access protocol is implemented by OSI layer 2. This pro-
tocol also includes data security and the handling of the transmission proto-
cols and messages.
The Medium Access Control (MAC) specifies the procedures which determine
when a device is permitted to transmit data. A token passing procedure is
used to handle the bus access between master devices, and a polling proce-
dure is used to handle the communication between a master device and its
assigned slave device(s).
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