Motorola MTR2000 T5544 Instruction / Field Service Manual page 180

Station Control Modules
Overview of Circuitry
2
The SCM contains the following circuitry:
• Host Microprocessor – that part of the MC68356 which serves as the central
controller for the station and the SCM
• Non-Volatile Memory – consists of Flash EPROM memory, containing both
the system operating software and the station codeplug data
• SRAM Memory – Static RAM serves as short term storage for data
• Digital Signal Processing (DSP) and DSP ASIC Circuitry – that part of the
MC68356 (and associated ASIC) which performs high-speed processing of
all audio and signalling data signals
• Station Reference Circuitry – generates the 2.1 MHz reference signal used
throughout the station
• Serial Peripheral Interface (SPI) Input/Output Circuitry – provides high-
speed serial bus to pass control and diagnostic information between the Host
microprocessor, the station modules (receiver, exciter, PA, etc.) and various
serially-controlled devices on the SCM
• Serial Input/Output Circuitry – provides bus circuitry to buffer two of the
Host microprocessor Serial Communication Interface (SCI) ports (SCC1
and SCC2) for communication with optional modules, and an external IBM-
PC running Radio Service Software (RSS)
• Audio Processing Circuitry – routes the various audio input signals (such as
microphone, wireline, and receiver audio) to output devices (such as external
speaker and exciter modulation inputs) and converts (via various codecs) the
audio signals between digital and analog formats for serial transmission to/
from the DSP
• Parallel I/O Circuitry – provides the necessary logic interface for the Host
microprocessor to send/receive miscellaneous control signals to/from vari-
ous station modules and externally connected equipment, and to control the
status LEDs on the front panel
• Supply Voltage Circuitry – contains filtering, voltage doubling and regulato-
ry circuitry which accepts various input voltages from backplane regulators
and the power supply, and generates the operating voltages required by the
Receiver and Exciter modules, and the SCM
68P81096E32-E
08/06/07