Siemens SIMATIC NET Manuel page 163

Safety guidelines
Warning!
v
The OLM/ELM units are designed for
operation with safety extra-low vol-
tage. Accordingly, only safety extra-
low voltages (SELV) to
IEC950/EN60950/VDE0805 may be
connected to the supply voltage
connections.
1. Functional description
1.1 GENERAL FUNCTIONS
Signal regeneration
The OLM/ELM processes the signal shape
and amplitude of the data received.
Retiming
In order to prevent jitter increasing over
several segments, the OLM/ELM retimes the
data to be transmitted.
Preamble regeneration
The OLM/ELM supplements lost preamble
bits from data received to 64 bits (incl. the
start of frame delimiter (SFD)).
Fragment extension
Collisions can cause short fragments to
occur. If the OLM/ELM receives a fragment,
this is supplemented to give the minimum
length of 96 bits. This ensures reliable colli-
sion detection by all network participants.
Collision handling
If the OLM/ELM detects a data collision, it
interrupts the transmission. For the
duration of the collision, the collided data
package is replaced by a jam signal to
ensure collision detection by the terminal
equipments.
Auto partitioning
Network failures can be caused by perma-
nent occupancy, interrupted lines, lack of
terminating resistors, damaged cable insu-
lation and frequent collisions due to electro-
magnetic interference. In order to protect
the network from such failures, the
OLM/ELM in this case separates the seg-
ment in the receiving direction from the rest
of the network.
The OLM/ELM has this auto partitioning
function individually at each port. The other
ports can thus continue to be operated
without interference if one of the ports has
been auto partitioned. In the event of auto
partitioning, transmission continues into
the ITP segment or the F/O line but recepti-
on at this port is blocked.
With twisted pair, auto partitioning is activa-
ted if
– a data collision lasts longer than 105 µs or
– there are more than 64 consecutive data
collisions.
With F/O, auto partitioning becomes active
when
– a data collision lasts longer than 1.5 ms
(normal mode) or 0.2 ms (redundant
mode) or
– there are more than 64 (normal mode) or
16 (redundant mode) consecutive data
collisions.
Reconnection
The segment is reconnected to the network
as soon as a package with the minimum
length of 51 µs is received without collision
at the relevant port, i. e. when the segment
is working properly again.
When the redundant mode is active, packa-
ges >51 µs sent at a F/O port without
collision also lead to reconnection.
Jabber control
Due to a defective bus coupler or LAN con-
troller, for example, the network can be con-
tinuously occupied with data. To protect
against this, the OLM/ELM interrupts
reception
– at the affected ITP or AUI port after 5.5
ms. 9.6 µs after the end of the error the
auto partitioning will be canceled.
(jabber lockup protection)
– at the relevant F/O port after 3.9 ms. 420
ms after the end of the error the auto par-
titioning will be canceled.
(Rx jabber)
1.2 SPECIFIC FUNCTIONS OF THE
ITP INTERFACE
Link control
The OLM/ELM monitors the connected ITP
line segments for short-circuit or interrupt
using regular link test pulses in accordance
with IEEE standard 802.3 10BASE-T. The
OLM/ELM does not transmit any data in an
ITP segment from which it does not receive
a link test pulse.
Note: A non-occupied interface is assessed
as a line interrupt. The ITP line to terminal
equipment which is switched off is likewise
assessed as a line interrupt as the de-
energised bus coupler cannot transmit link
test pulses.
Auto polarity exchange
If the reception line pair is incorrectly
connected (RD+ and RD- switched) polarity
is automatically reversed.
1.3 SPECIFIC FUNCTIONS OF THE
F/O INTERFACE
Link control
The OLM monitors the connected F/O lines
for interrupts using regular link test pulses
in accordance with IEEE standard 802.3
10BASE-FL. The OLM transmits no data to
an F/O line from which it is receiving no link
test pulse.
Redundancy
In areas where data security has top priori-
ty, it is possible with the aid of the redun-
dancy function to bridge any failure of an
F/O line or OLM. To do so, a replacement
line is frequently routed in a different cable
run. In the event of a fault, there is an auto-
matic switch between the main line and the
replacement. A cross-link within the bus
structure creates a ring (see Fig. 6). If any
OLM link or OLM fails, every other OLM can
still be reached with the aid of the redun-
dant run.
1.4 DISPLAY ELEMENTS
Equipment status
The 4 LEDs on top provide information
about statuses which affect the function of
the entire OLM/ELM.
P1 – Power 1 (green LED)
– lit: supply voltage 1 present
– lit not: – supply voltage 1 not present,
– hardware fault in OLM/ELM
P2 – Power 2 (green LED)
– lit: supply voltage 2 present
– lit not: – supply voltage 2 not present,
– hardware fault in OLM/ELM
DA – Data (yellow LED)
– lit: OLM/ELM receiving data at at least 1
interface
– lit not: – OLM/ELM not receiving data at
any interface,
– hardware fault in OLM/ELM
Depending on network load, the illuminati-
on of the LED can vary between a brief
lighting up to permanent illumination.
CD – Collision Detect (red LED)
– lit: data collision detected at OLM/ELM
level
– lit not: – no data collision at OLM/ELM
level
Port Status ELM
These groups of LEDs display port-related
information.
LS1 to LS3 - link status of the ITP
ports (3 x green LED)
– lit: ELM receiving link test pulses from
ITP segment,
– the ITP segment connected is
working properly
– lit not: ELM is not receiving any link test
pulses from ITP segment,
– the assigned ITP port is not
connected,
– the equipment connected is
switched off,
– the ITP line is interrupted or
short-circuited
Port Status OLMV2.0
These groups of LEDs display port-related
information.
LS1 to LS3 - link status of the ITP
ports (3 x green LED)
– lit: OLM receiving link test pulses
from ITP segment,
– the ITP segment connected is
working properly
– flashes 2 times
per period: port has auto partitioned
– lit not: OLM is not receiving any link test
pulses from ITP segment,
– the assigned ITP port is not
connected,
– the equipment connected is
switched off,
– the ITP line is interrupted or
short-circuited
LS4 – link status of F/O port 4
(green LED)
– lit: OLM receiving link test pulses
from F/O segment,
– the F/O segment connected is
working properly
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