Motorola MTR2000 T5544 Instruction / Field Service Manual page 189

Parallel I/O Circuitry
68P81096E32-E
08/06/07
Wireline Interface Board Audio
Each of the wireline inputs/outputs has a programmable gain stage on the Wireline
Interface Board (WIB). Digitized audio is carried to/from the DSP ASIC via the
PCM Codec bus. When the line 1/2 pair carries narrow-band audio, the audio is
converted to/from digital format by a PCM Codec on the WIB.
For the 8-wire model WIB, the line 3/4 pair are restricted to narrow-band audio,
and are converted to/from digital format by a PCM Codec on the WIB.
MRTI Audio
MRTI audio is handled by Codec #2. In most installations, the MRTI is a half
duplex device. This allows MRTI TX Audio to be routed to the local speaker (and
thus to the MRTI RX AUDIO line) without causing echo problems (since the
MRTI RX AUDIO line is muted in the MRTI). Gain in the MRTI paths is set by
station software.
Full duplex MRTI operation is available, with the limitation that MRTI TX Audio
does is not heard from the local speaker.
Trunking Audio
A trunking station can operate as either a control channel or a voice channel. In
either case, wideband audio is routed to/from the Trunking Central Controller
(TCC) as Trunk TX Data (through Codec #1) and Trunk RX Data (through Codec
#5), providing paths for control and status tones. For voice channel operation,
voice audio is routed to the WIB as described in the Wireline Audio section.
Exciter Modulation Signals
Digitized audio/data intended to be transmitted from the station is output from the
DSP circuitry to Codec #1. The digitized signal is converted to analog, level shift-
ed and amplified. The output is then fed to one of the inputs of a multiplexer
switch. The output of the multiplexer is fed to two individual digitally-controlled
potentiometers (each of which is adjusted by the Host μP via the SPI Bus) and out-
put to the Exciter Module as modulation signals VCO MOD AUDIO and REF
MOD AUDIO.
General
The Parallel I/O circuitry allows the Host μP to generate SPI bus chip selects and
to send/receive control signals to/from station modules and external options (via
the backplane).
Station Control Modules
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