June 15, 2005
6815854H01-A
3-72
Theory of Operation:
Controller Section
• LV Frac-N (U6751) (microcontroller only writes to IC): scales the frequency from the VCO,
control RX, and TX feedback loops
• EPOT (U0206) (microcontroller only writes to IC): controls the 32 steps of audio volume (vol=0:
low to 15: high) that is routed to audio PA
3.14.9 Receive Audio
The controller processes all received signals digitally. This requires a unique back-end from a
standard analog radio. This unique functionality is provided by the ABACUS III IC as the interface to
the DSP. The ABACUS III IC (in the receive back-end section of the transceiver) provides a digital
back-end for the receiver. It provides digital output data words at a 20 kHz sampling rate (refer to
section
for more details on ABACUS III IC operation). This data is passed
to the DSP through the RX Baseband Interface Port (BBP). The SPI bus is used to configure the
operation of the ABACUS III IC and is driven by the Patriot IC. ABACUS_DIN is the data line on
which the RX data words are transferred from ABACUS III IC to the Patriot IC (refer to
).
Figure 3-48. XTL 1500 RX Signal Path
The ABACUS III data is transferred to the Patriot IC at a 1.2 MHz bit rate, which is a synchronous
clock provided by the ABACUS III IC. The 20 kHz interrupt clock, also provided by the ABACUS III
IC, signals the arrival of a data packet and represents the sampling rate of the received data.
The DSP then processes this data to extract audio and signaling, perform filtering, alert-tone
generation, etc. The DSP performs de-emphasis and discrimination before sending the discriminator
data to the audio CODEC (U0200) via the SAP SSI bus. This bus is the digital audio bus consisting
of the 512 kHz master bit clock (SAP_DCLK), and the 8 kHz frame sync (SAP_FSYNC). These
clocks represent the data bit rate and sampling rate, respectively, for both the transmit and receive
digital audio. For secure messages, the digital signal data must be passed to the secure module for
decryption prior to DSP processing of the speaker data. The DSP transfers the data to and from the
secure module through the SAP SSI port TXD and RXD signals. Configuration and mode control of
the secure module is performed by the MCU through this bus.
Patriot
U100
SPI
SAP
BBP
RF IN
SPKR+
SPKR -
CODEC
U0200
ABACUS III
U6000
Volume Pot
U0206
Audio PA
U0204
SCKA
SRDA
SCKA
SC0B
SRDB
SC1B
S PI_SC
SPI_MOSI
SPI_MISO
MCLK
DT
FSR
RO NEG
1.2MHz
RX Data
20kHz
ABA_CLK
ABA_RXD
ABA_FSYNC
(J0401-4)
(J0401-4)
512kHz
TX Data
8kHz
PD
PC
MAEPF-27891-O
Содержание XTL 1500
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