P R O F I B U S P
O W E R
H
U B
S
E G M E N T
C
O U P L E R
PROFIBUS Commissioning
Subject to reasonable modifications due to technical advances.
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.11
While on other tools, the response monitor is preset individually for each
PROFIBUS PA participant. The response monitor value does not chan-
ge in any way.
Many tools calculate the time T
WD
automatically with a corresponding
baud rate based on the cycle time of the master.
If the baud rates at the PROFIBUS DP end are high (e.g. 12 MBd), the
cycle times of the PA end may be 300 times longer. If a PROFIBUS PA
device has been programmed directly with a time T
WD
calculated at a
higher master baud rate (DP), this is usually shorter than the PA cycle
and the device does not exchange data.
The following bus parameters should be used to ensure the DP/PA ga-
teway operates reliably:
•
only one watchdog time T
WD
is programmed for the entire
PROFIBUS system. The longest delay period must be determi-
ned in order to define T
WD
•
one watchdog time T
WD
is programmed for each individual sla-
ve.
The preset (parameterized) time T
WD
must be greater than the maxi-
mum occurring delay period T
V_max
.
Two types of Watchdogs can be configured on the HD2-GTR-4PA in cy-
clic or acyclic data exchange (chapter “Watchdog Time in the DTM” on
page 48):
•
Transparent Watchdog: The Watchdog time on the DP side is
the same as on the PA side (= default setting).
•
Fixed Watchdog: A Watchdog time is set on the HD2-GTR-4PA
for the PA side that is different than the DP side.
5.2.3
Information about I/O Cycle Time
The overall I/O data cycle time from a DP master via HD2-GTR-4PA to
a PA slave can be approximated as follows:
T
Cycle_IO_Data
= T
Cycle_DP
+ T
Cycle_PA_Channel
where:
T
Cycle_PA_Channel
= Cycle time of the PROFIBUS PA channel
T
Cycle_DP
= Cycle time of the PROFIBUS DP
The HD2-GTR-4PA measures the current cycle time of each PA segment
and generates a diagnostic message if the Watchdog time is too short.
Then the Watchdog time must be increased. The Gateway diagnostics
are based on the following formula: 2 x T
Cycle_PA_Channel
+ 500 ms
Note
