Device types
Section 1-3
4
1-3
Device types
Master devices
Active stations
DPM1, DPM2
Slave devices
Passive stations
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.
There are two types of master devices: DP master class 1 (DPM1) and DP
master class 2 (DPM2). A DPM1 is a central controller which exchanges
information with the decentralised stations (i.e. DP slaves) within a specified
message cycle. DPM2 devices are programmers, configuration devices or
operator panels. They are used during commissioning for configuration of the
DP system or for operation and monitoring purposes.
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.
The C200HW-PRM21 is a DPM1 device.
1-4
PROFIBUS-DP characteristics
1-4-1
Bus Access Protocol
Layer 2
Medium Access Control
Token passing
Polling procedure
The bus access protocol is implemented by layer 2. This protocol also
includes data security and the handling of the transmission protocols and
telegrams.
The Medium Access Control (MAC) specifies the procedure when a station is
permitted to transmit data. The token passing procedure is used to handle the
bus access between master devices and the polling procedure is used to
handle the communication between a master device and its assigned slave
device(s).
The token passing procedure guarantees that the bus access right (the token)
is assigned to each master within a precisely defined time frame. The token
message, a special telegram for passing access rights from one master to the
next master must be passed around the logical token ring - once to each
master - within a specified target rotation time.
The polling or master-slave procedure permits the master, which currently
owns the token, to access the assigned slaves. The picture below shows a
possible configuration.
Содержание C200HW-PRM21
Страница 1: ...C200HW PRM21 PROFIBUS DP Master Unit OPERATION MANUAL Cat No W349 E2 2...
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Страница 5: ...C200HW PRM21 PROFIBUS DP Master Unit Operation Manual Produced May 2000...
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Страница 126: ...Authorised Distributor Cat No W349 E2 2 Note Specifications subject to change without notice Printed in the Netherlands...