C903
1228-1147 rev. 1
FUNCTIONAL OVERVIEW
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External Connectors
External units are connected to the transceiver by means of a 12-pin connector on the
bottom of the phone.
System connector pin input/output overview:
Clocks
Clock Distribution
The clocking for the access and application subsystems is separated. This means that the
subsystems can wake up or go to sleep mode independently. The access subsystem is
clocked by the 26 MHz Voltage Controlled Crystal Oscillator (VCXO) located in the
GSM/EDGE circuit. When the access subsystem has a job to do, the Master Clock (MCLK)
signal is requested from the RF part. Most other clocks needed within the access
subsystem are generated from the MCLK. Some minor parts like sleep timer and cable
detect use the 32 kHz real-time clock. The 32 kHz real-time clock clocks the application
subsystem, and all other internal clocks needed within the application subsystem are
generated from this clock. However, when audio is transferred between the application
and the access subsystems, the MCLK is used.
Master Clock
(26 MHz)
The 26.00 MHz VCXO-based MCLK is distributed as a square wave signal from the
GSM/EDGE circuit. In order to have full control over the load on the MCLK, only the access
side of the digital baseband controller is allowed to request the MCLK. However, by
indirect means also the application side CPU can issue the request. A VCXO-based square
wave is also distributed to the WCDMA circuit, but is turned on only upon a command
from the digital baseband controller.
Real-time Clock
(32. 768 kHz)
A 32.768 kHz crystal oscillator provides a low frequency clock whenever the platform has
power. This clock is used to keep the Real-Time Clock (RTC) block functioning, so that the
platform can keep track of the time and date. The low frequency clock is generated in the
analog baseband controller and distributed to the digital baseband controller, and if
necessary to external devices like Bluetooth, FM radio and A-GPS.
A-GPS
The Assisted GPS functionality in the phone is realized with the Global Locate
Hammerhead GPS module. The Global Locate Hammerhead belongs to the Type 2 GPS
solutions. The PMB 2525 Hammerhead II GPS IC is a GPS single chip device containing a
complete radio frequency front-end as well as the signal processing functionality in a
single die. The device allows the usage of assistance data by supporting A-GPS (assisted
GPS) standards (RRLP, RRC, OMA SUPL). One of three serial interfaces, UART, I²C or SPI,
is used for communication with the host system.
Clock Reference Frequency
The platform provides two reference frequencies, a 32.768 kHz clock (RTCCLK) from the
Analog Baseband Controller, and a 26 MHz reference clock (SYSCLK) from the Digital
Baseband Controller. The RTCCLK is used by the phone real time clock function. The
RTCCLK is distributed to the A-GPS module as a logical square wave. SYSCLK is derived
from the reference modulation clock MCLK to the platform access system and is
distributed from the Digital Baseband Controller to the A-GPS module. This 26 MHz clock
is synchronized with the cellular network to an accuracy of ±0.1 ppm. Automatic
frequency updates can also cause large frequency corrections, with associated phase
discontinuities. In order to isolate the A-GPS module for the unstable effects of SYSCLK,
an external reference clock is required. This external reference frequency provided by a
TCXO is required to provide a clock with very high short term stability. The frequency of
the TCXO is calibrated against the cellular reference clock by the A-GPS module enabling
the use of a more economical less accurate TCXO.
Interface and Control
The Interface and control consists of system timing and control. The control interface
includes a communication link where both data and control information are transferred
between platform and the A-GPS module. Data and command information is transferred
using a full-duplex Universal Asynchronous Receiver Transmitter (UART) interface.
Other control signals include the following:
• A GPIO or platform reset used as a reset signal (nRESET) to the GPS module.
• A Transmission On signal (TXON/ RX_HOLD), is used to indicate to the A-GPS module
when the ME is transmitting. The A-GPS modules receiver is disabled whilst the ME is
transmitting.
• A hardware timing pulse (GPSSTART/SYNC) providing the A-GPS module with a
highly accurate timing reference. The A-GPS is able to accurately synchronize its
GPS time to this reference pulse.
• A GPIO used as an enable (POWERON) signal to the GPS module.
• A GPIO used for power control for the GPS module.
A-GPS Block Diagram:
Technical Description
SEMC Troubleshooting Manual
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