Motorola ASTRO Digital Saber Service Manual page 52

samples, the DSP reads the microphone samples from registers
mapped into it's memory space starting at Y:FFF0. The ADSIC provides
an 8kHz interrupt to the DSP on IRQB for processing these
microphone data samples.
As with the received trunking low speed data, low speed data is
processed by the MCU and returned to the DSP at the DSP SCLK port
connected to the MCU port PA0.
For secure messages, the analog signal may be passed to the secure
module for encryption prior to further processing. The DSP transfers
the data to and from the secure module through it's SCI port
consisting of TXD and RXD. Configuration and mode control of the
secure module is performed by the MCU through the SPI bus.
The DSP processes these microphone samples and generates and mixes
the appropriate signaling and filters the resultant data. This data is
then transferred to the ADSIC IC on the DSP SSI port. The transmit
side of the SSI port consists of SC2, SCK, and STD. The DSP SSI port is
a synchronous serial port. SCK is the 1.2MHz clock input derived from
the ADSIC which makes it synchronous. The data is clocked over to
the ADSIC on STD at a 1.2MHz rate. The ADSIC generates a 48kHz
interrupt on SC2 so that a new sample data packet is transferred at a
48kHz rate and sets the transmit data sampling rate at 48Ksp. These
samples are then input to a transmit D/A which converts the data to
an analog waveform. This waveform is actually the modulation out
signal from the ADSIC port VVO and is connected directly to the VCO.
The transmit side of the transceiver is virtually identical to a standard
analog FM radio.
Also required is the 2.4MHz ODC signal from the ABACUS IC.
Although the ABACUS IC provides receiver functions it is important to
note that this 2.4MHz reference is required for all of the ADSIC
operations.
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