Motorola MTR2000 T5544 Instruction / Field Service Manual page 198

CLN1204 Wireline Interface Board
Description of Audio/Data Signal Paths
Note
!
CAUTION
4
For 2-wire and 4-wire configurations, phone line connections are made at
the wire-trap terminal connector on the station backplane, with the re-
quired line impedance match being selected on the WIB. 2-wire audio con-
nections are made at Line 2 Audio.
Refer to Figure 2 for the correct settings of impedance matching jump-
ers, as determined by the country in which the station is being operated.
Incorrect jumper settings may violate local telecommunications author-
ity regulations and place the equipment in an unapproved status. Some
countries also specify a maximum allowed line input level. Refer to the
RSS Online Help, under Line Level.
Coarse gain adjustments are provided by circuitry on the WIB for Land-
line-to-Station and Station-to-Landline audio paths. Additional fine level
adjustments are performed in software in the Station Control Module.
2-Wire Voice Audio Path (Refer to Figure 3)
Voice audio signals sent to/from the station via 2-wire copper pair are pro-
cessed by the 2-wire audio circuit on the WIB (Line 2 Audio). The audio
transformer in this circuit may have both inbound and outbound audio
signals present simultaneously. In this case, the outbound and inbound
signals are mixed and routed via the inbound audio path to the SCM,
where an adaptive cancellation routine in the DSP isolates the inbound au-
dio. The 2-wire audio circuit operates as follows:
Landline-to-Station balanced audio is input to the primary of an audio
transformer. The signal is induced into the transformer secondary and fed
to a buffer. (Note that jumpers in parallel with the transformer primary
and secondary provide for selectable impedance matching. Refer to Fig-
ure 2 for impedance matching information.)
The buffer sums the inbound and outbound signals and feeds this signal,
via an analog switch (not shown), to pre-emphasis and gain adjust circuit-
ry. To compensate for line losses, the gain adjust circuitry provides coarse
adjustment for eight levels of gain adjust (5, 10, 15, 20, 25, 30, 35, and 40dB)
which is under the control of the SCM (via the SPI latch).
The output of the gain adjust circuitry is de-emphasized and then fed to an
A/D converter in the PCM codec, which digitizes the audio signal into a
PCM output. This output is fed serially to the DSP ASIC on the SCM,
which provides a memory-mapped interface with the DSP and other SCM
audio circuitry (refer to the Station Control Module section).
Station-to-Landline audio is input to the WIB as PCM data (WL 1/2 RXD)
and fed to a D/A converter in the PCM codec, which takes the PCM data
and converts it to an analog audio signal. The audio signal is fed to gain
68P81096E28-C
09/30/05