ProSoft Technology PS69-DPS - Manual (Page 73)

PS69-DPS ♦ CompactLogix or MicroLogix Platform Reference
Profibus DP Slave Communication Module User Manual
ProSoft Technology, Inc. Page 73 of 108
May 9, 2014
5.3 PROFIBUS Functionality
5.3.1 DPV0 Services
DPV0 services in PROFIBUS refer to the cyclic data exchange mechanism
between a class 1 master and a network slave. PROFIBUS-DP defines two types
of masters. The class 1 master handles data communication with slaves
assigned to it. A class 2 master should only be used for commissioning
purposes. In a PROFIBUS telegram, class 1 masters and slaves transmit up to
244 bytes per telegram. Valid station addresses on PROFIBUS range from 0 to
125.
Fail Safe Mode
For safety reasons, the PROFIBUS master informs connected slaves of its
current control status at certain intervals using a "Global Control" telegram. If the
master goes to Clear Mode, the Fail Safe enabled slaves will switch to a Fail
Safe state. Slaves capable of the Fail Safe state can be configured to either to
hold the last state of the outputs or set its outputs to "0". Slaves that do not
support the Fail Safe state set their outputs to "0".
Global Control
With the Global Control telegram, the master can send unsolicited commands
like Sync/Unsync, Freeze/Unfreeze and Clear Data to a slave or a group of
slaves for synchronization purposes. Group membership is defined during
network start-up and can be set in the master configuration tool.
Sync and Freeze
Sync and Freeze are optional commands and slaves do not need to support
them. However, they must be able to process the Global Control telegram. With a
Freeze command, the master prompts a slave or a group of slaves to "freeze"
their inputs to the current state. A Sync telegram causes the current output data
to latch at their current state until the next Sync telegram arrives. Unfreeze and
Unsync cancel each corresponding state.
Extended Device Diagnostics
Using diagnostic telegrams, the slave informs the network master of its current
state in a high-priority telegram. The first 6 bytes of the diagnostic telegram are
comprised of information such as its identity code ("Ident Code") or
correct/incorrect configuration. The remaining bytes of this telegram are referred
to as Extended Device Diagnostics and they contain information that is specific to
the particular slave.