Motorola ASTRO Digital XTL 5000

May 25, 2005 6881096C74-B
3-72 Theory of Operation: Controller Section
Figure 3-48. Serial Peripheral Interface (SPI) Block Diagram
The following ICs are controlled and programmed by SPI_A:
• ABACUS III (U6000): Sigma Delta A/D converter and 2nd LO frequency adjust. The
ABACUS III IC has a single pin for both input and output. Therefore, additional circuitry (U0103
and U0105) handles the SPI_MISO or the SPI_MOSI data lines from the microcontroller and
allows a read or write operation to occur with the ABACUS III IC via a single bidirectional data
line.
• A/D (U0953): monitors temperature, source voltage, PA current, feedback-voltage loop,
forward-detected voltage, and reverse-detected voltage
• D/A (U0959) (microcontroller only writes to IC): controls bias stages 1-4, sets current limit,
monitor thermistors, tuner overall RF power, and adjusts RX filter
• 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
3.8.10 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 “3.5. Receiver Back-End” 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 3-49
on page 3-73).
PATRIOT
U100
QSCKA
MOSIA
SPICS8
MISOA
SPICS4
SPICS6
SPICS9
SPICS5
SCKA
MOSIA
SCKA
MISOA
MOSIA
SYN_SEL*
ABACUS3_CS*
LV FRAC-N
U6751
ABACUS
U6000
SCKA
MOSIA
MISOA
AD_EN*
A/D
U0953
SCKA
MOSIA
SCKA
EEPOT_3_CS*
MOSIA
DA_EN*
LOG POT
U0206
D/A
U0959
MAEPF-27820-O