ProSoft Technology PS69-DPM - Manual (Page 109)

PS69-DPM ♦ CompactLogix or MicroLogix Platform Contents
PROFIBUS DPV1 Master User Manual
ProSoft Technology, Inc. Page 109 of 130
October 1, 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 PROSOFT.fdt (SYCON.net) and is
transmitted 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".
6.2.2 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.
6.2.3 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 module and all Slave devices connected,
is stopped. All slaves will clear their outputs and the Master will be in Stop mode. This
control bit allows the user program to make a controlled start of the communication with the
PROFIBUS system.