Motorola MTR2000 T5544 Instruction / Field Service Manual page 187

Audio Processing Circuitry
Note
68P81096E32-E
08/06/07
DSP ASIC
The DSP ASIC operates under control of the DSP to provide a number of func-
tions, as follows:
• Interfaces with the DSP via the DSP address and data buses and interrupt re-
quest lines
• Accepts 16.8 MHz signal from Station Reference circuitry and outputs a
2.1 MHz reference signal used throughout the station, and a 1.2 MHz pro-
cessor clock used by the MC68356 to generate the core clocks for the DSP
and Host μP.
• Provides serial interfaces for linear Codec #5 and PCM codecs
• Provides serial interface for programming custom IC on Receiver Module,
and accepts digitized data from custom IC via differential-to TTL converter
circuitry
• Provides Receiver Signal Strength Indication (RSSI) data ouput
General
The Audio Processing circuitry interfaces external analog audio inputs and out-
puts with the DSP circuitry. The CLN1465 uses two linear codec ICs (referred to
as Codec #1 and Codec #5) to handle wideband codec operation and the additional
signal line requirements of trunking operation. Since audio signals input to or out-
put from the DSP are in a digitized format, the codecs convert the audio signals
between analog and digital formats as required.
Microphone and MRTI audio signals are digitized by Codec #2 (p/o Audio Pro-
cessing Circuitry) before being sent to DSP ASIC via PCM Codec Bus
Speaker Audio
Speaker audio (to external speaker) is provided by codec #2. This signal is shared
with MRTI RX Audio. The MRTI level is set (via the RSS) to suit MRTI output
requirements. The adjustment is accomplished using a digital potentiometer
which is controlled by the Host μP (via the SPI bus).
When the station is configured for operation with a full-duplex MRTI unit (the de-
fault is half-duplex), MRTI TX Audio is not routed to the speaker to prevent echo
problems on the phone line. However, this also prevents use of the local micro-
phone input and external speaker for MRTI testing.
Since trunking and MRTI share the same backplane connector, they are mutually
exclusive.
Station Control Modules
9