Installation guide

LTU/NTU SZ-DOC-W5-1.pd
f
Operating Manual
V
ersion: 1.5
Revision: 2002-09-10 28
ACU
Tx A Tx B Rx A Rx B
LTU
Tx A
…
CMU
Tx B Rx A Rx BTx A Tx B Rx A Rx B
Front
Connector
Backplane
Connector
EIA-485
Backplane
Bus
Tx B Rx A
Subrack 0
Subrack 1
Rx B
ACU
Tx A Tx B Rx A Rx B
LTU
Tx A
…
LTU
Tx B Rx A Rx BTx A Tx B Rx A Rx B
Front
Connector
Backplane
Connector
EIA-485
Backplane
Bus
Tx B Rx A Rx B
X.2
5
or LAN
Management
Center
Figure 3-15: TMN Bus 2-Wire Connection for Plug-in Units
Limitation:
Plug-in versions of CMU, ACU and LTU support 2-wire connection only
In case of a single subrack configuration and if no external alarm indications have to be
controlled, an ACU is not needed in the subrack. But direct access for configuration of LTUs via
the monitor interface on a local craft terminal is not possible without an ACU.
3.6.3 TIA/EIA-485 Bus Termination
In order to achieve highly reliable connections with a minimum of reflections, a termination with
120Ω is required at both ends of the bus by the TIA/EIA-485 standard.
A bus termination is not imperative when transmission is applied over short distances (< 1m)
and with signaling rates ¼200 kbit/s.
The TMN bus communication is running with a signaling rate of 5 kbit/s. Due to this fact a
termination is required only if TMN bus is extended via cable over long distances and especially
if different reference ground levels are applied at both ends of the bus (different racks).