Prosoft-technology PS69-DPS User Manual download pdf (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.

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Prosoft-technology PS69-DPS User Manual Page 73