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PROFIBUS Communication
WL Circuit Breaker
Shortly before 30 minutes have
elapsed (29:50), a SYNC command
is sent to all the devices in question.
The bit for synchronizing the clocks
(bit 7 of byte 1 of the control byte)
is then set (29:55).
With millisecond accuracy, a SYNC
command is sent again on the half
hour (30:00). In this way, the clocks
for all the devices within the SYNC
group are rounded up or down to
the half hour. Synchronization is
not carried out on the hour because
clocks that are fast would then be one
hour ahead of clocks that are slow.
An UNSYNC command must then be
sent and the synchronization bit (bit 7
of byte 1 of the control byte) reset so
that data exchange can continue.
This procedure should be carried out
regularly on a time-controlled basis,
for example, by GPS in an S7.
3/15
Diagnostic Message
By requesting the diagnostic data,
the DP master checks at start-up
whether the DP slave exists and is
ready to be parameterized. The
diagnostic data from the DP slave
comprises a diagnostic data part
defined in EN50170 and specific
DP slave diagnostic information.
The DP slave uses the diagnostic
data to report its operating status
(PROFIBUS-DP) to the DP master
and, in the event of a diagnosis, the
reason for the diagnostic message. A
DP slave can report a local diagnostic
event to the DP master via the layer-2
message priority "high prio" of the
Data_Exchange response message
in layer 2. The DP master then
requests the diagnostic data from
the DP slave for analysis. If no current
diagnostic events are present, the
Data_Exchange response message is
"low prio." The diagnostic data of a
DP slave can be requested at any time
by a DP master without necessarily
reporting diagnostic events.
Diagnostic message for S7 stations
Diagnostics-capable modules in
distributed peripheral devices can
report events, such as a partial
station failure, wire breakage in
signal module, periphery channel
short-circuit/overload, or a load
voltage supply failure, using a
diagnostic alarm. With an incoming
and outgoing diagnostic alarm, the
organizational block for diagnostic
alarm OB82 is called by the CPU
operating system. If a diagnostic
alarm occurs and OB82 is not
programmed, the CPU switches
to the STOP status.
A failure (incoming event) or
restoration (outgoing event) of a
DP slave is reported by the operating
system of the S7 CPU via OB86. If
OB86 has not been programmed,
the S7 CPU switches to the STOP
status if an event occurs.
WL PROFIBUS Communication and Electronic Accessories • July 2004
Diagnosing the WL Circuit Breaker
In accordance with the relevant
standards, the slave reports an
external diagnostic message to
the PLC master when it sets byte
0 to "08" instead of "00." This is
generated automatically by the ASIC.
If an external diagnostic message is
present, byte 7 is set to "01" instead
of "00" to indicate that an external
diagnosis is present.
The external diagnosis in the WL is
only triggered in one of the following
statuses:
• The COM15 module is not ready
for operation
• Bit 18.2 and/or 18.3 report a
number that is not 0 (a
maintenance message)
• Bit 18.4 is set, indicating the circuit
breaker is not present
• One of the bits in byte 19 = "1"
In bytes 24 to 27, the presence of a
module is entered on the CubicleBUS.
If a module is added, removed, or
identified as faulty, the corresponding
bit in byte 19 (19.2, 19.3, 19.4)
is set and the affected module
indicated in bytes 20 to 23. An
incoming (i.e. 08 0C 00 xx 80 C0 42
01 05 82 00 00 00 0F 81 01 00...)
diagnostic message is then triggered
on the PROFIBUS-DP. If the module
that triggered the diagnosis does not
change in any other way, the message
becomes an outgoing message after
10 seconds (provided that no other
reasons for a diagnosis exist:
00 0C 00 xx 80 C0 42 00 05 82 00
00 00 0F 81 01 00...). The
information on the last change
(19.2, 19.3, or 19.4 plus module
number bytes 20 to 24) remains
until another message is received. If
a module is added, the corresponding
module is indicated in bytes 20 to 24.
In the list of modules present, the
module that has been added will
not appear until after the outgoing
diagnostic message has been
processed (10 seconds). The user
can always see which module was
last added to the CubicleBUS.
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