Prosoft-technology PS69-DPS User Manual download pdf (Page 74)

Reference PS69-DPS ♦ CompactLogix or MicroLogix Platform

User Manual Profibus DP Slave Communication Module

Page 74 of 108 ProSoft Technology, Inc.

May 9, 2014

Watchdog

Using the Watchdog functionality a network slave is able to monitor bus traffic in

order to ensure that the network master is still active and process data sent and

received are still being updated. The Watchdog time is configured in the master

config tool and is transmitted from the master to the slave during the network

start-up phase. If the Watchdog time out has been reached the slaves go to their

Fail Safe state (if supported) or set their outputs to "0".

5.3.2 DPV1 Services

As an addition to cyclic DPV0 services, non-cyclic services called Read, Write

and Alarm were added to PROFIBUS. These services are referred to as DPV1.

With DPV1, it is possible to address individual modules within the slave. In

addition, DPV1 services allow transferring non-time critical data to slaves who

require a large amount of configuration data or slaves that have to change

measurement ranges during runtime. DPV1 data exchange takes place after

cyclic data exchange in a PROFIBUS network cycle.

Read Request

With a Read Request telegram, the class 1 master can read data addressed by

slot and index within the data range of a slave device. This may take several

DPV0 cycles. If the master discovers a timeout, it aborts both DPV1 and DPV0

communication with the slave. Then the communication to the slave has to be re-

established. The master initiates the Read Request service.

Write Request

With a Write Request telegram, the class 1 master can write data addressed by

slot and index into the data range of a slave device. The timeout handling is

identical to the Read Request. The master initiates the Write Request service.

Alarm Indication

DPV1 Alarm handling is an addition to the Device Diagnostic function in

PROFIBUS. Alarms are reported to the master as device specific diagnostic

information. Therefore, the slave initiates an Alarm Indication. Other than Device

Diagnostic messages, Alarms have to be acknowledged by the Master.

5.3.3 Start/Stop Communication

Start/Stop communication with one bit: With the "NRDY" (NotReady) Bit the user

program can start or stop communication with the PROFIBUS-DP system. When

this Bit is set from the user program, the communication between the slave and

the master is stopped and will activate diagnostic request which is reported to the

PROFIBUS master during runtime. The cyclic data exchange will be suspended

and the module switches into a diagnostic mode and reports static diagnosis to

the master. This control bit allows the user program to make a controlled start of

the communication with the PROFIBUS system.

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