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B .
MODEM LINE UNIT
A modem line unit (MLU) is a board that is used to make it possible to use a modem as a
common pool resource. This board controls a maximum of 4 modems. The communication
between the MLU and the modem can be synchronous or asynchronous.
For each modem the MLU has two ports: one port with the V.24 interface to the modem and
one port with the analogue (2 or 4 wire) interface to the same modem. Both ports are
available at F122 front connectors:
MODEM
NUMBER
0
1
2
3
Table B-1 Front connector positions on MLU.
In the Hardware Manual and in the Installation Manual the layout of the front connector for
the V.24 interface is illustrated.
The analogue line to the modem can be 2-wire or 4-wire and this type must be set accordingly
by means of straps on the MLU. The straps are numbered X1.1 to X1.8:
-
X1.1 and X1.2 for modem number 0;
-
X1.3 and X1.4 for modem number 1;
-
X1.5 and X1.6 for modem number 2;
-
X1.7 and X1.8 for modem number 3.
The board positions of the straps and the correct settings for 2-wire or 4-wire operation are
given in the Maintenance Manual.
To be able to adapt the receive level of the input signal on the analogue line of a modem, the
PAD belonging to this line can be set to one of three levels: -25 dBr, -28 dBr or -31 dBr. By
means of one strap the detection level can be determined per modem. The straps are
numbered X2.1 to X2.4:
-
X2.1 for the detection level for modem number 0;
-
X2.2 for the detection level for modem number 1;
V.24 PORT AT
CONNECTOR
FBA
FBB
FBC
FBD
ANALOGUE LINE AT
CONNECTOR
FCA
FCB
FCC
FCD
67
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