Nokia 6255 Guide

Nokia Customer Care
6255/6255i6256/6256i (RM-19)
Mobile Terminal
Issue 2 05/2005 Company Confidential ©2005 Nokia Corporation
Baseband Description and
Troubleshooting

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Baseband Description and Troubleshooting Nokia Customer Care
Page 2 ©2005 Nokia Corporation Company Confidential Issue 2 05/2005
Contents Page
Introduction ..................................................................................................................................................... 4
Power Up and Reset ....................................................................................................................................6
Power Up - Power Key............................................................................................................................. 8
Power Up - Charger Connection .......................................................................................................... 8
Power Up - RTC Alarm............................................................................................................................. 9
Power Off .......................................................................................................................................................9
Power Consumption and Operation Modes .........................................................................................9
Power-off Mode........................................................................................................................................ 9
Sleep Mode.............................................................................................................................................. 10
Active Mode ............................................................................................................................................ 10
Charging Mode....................................................................................................................................... 10
Power Distribution ....................................................................................................................................11
Clock Distribution ......................................................................................................................................13
RFClk (19.2MHz Analog)...................................................................................................................... 13
RFConvClk (19.2MHz Digital)............................................................................................................. 14
CBUSClk Interface ................................................................................................................................. 15
DBUS Clk Interface................................................................................................................................ 16
SleepCLK (Digital) .................................................................................................................................. 17
SleepCLK (Analog).................................................................................................................................. 18
Flash Programming ...................................................................................................................................18
Connections to Baseband.................................................................................................................... 18
Baseband Power Up .............................................................................................................................. 18
Flash Programming Indication........................................................................................................... 19
Flashing..................................................................................................................................................... 19
Flash Programming Error Codes ........................................................................................................ 22
Charging Operation ...................................................................................................................................24
Battery ...................................................................................................................................................... 24
Charging Circuitry ................................................................................................................................. 24
Charger Detection.................................................................................................................................. 25
Audio .............................................................................................................................................................25
Displays and Keymat ................................................................................................................................25
Main Display............................................................................................................................................ 26
Secondary Display.................................................................................................................................. 27
Keymat...................................................................................................................................................... 27
Camera .........................................................................................................................................................27
DC Measurements.................................................................................................................................. 28
AC Measurements.................................................................................................................................. 28
FM Radio ......................................................................................................................................................29
FM Radio Test ......................................................................................................................................... 29
USB Interface ..............................................................................................................................................31
Accessories ..................................................................................................................................................33
Charging................................................................................................................................................... 34
Pop-port Headset Detection............................................................................................................... 36
FBus Detection........................................................................................................................................ 36
Accessory Detection Through ACI..................................................................................................... 37
RUIM (SIM CAR) ........................................................................................................................................39
Main Display Test Points ........................................................................................................................... 40

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Secondary Display Test Points.................................................................................................................. 45
GPS Module .................................................................................................................................................48
Troubleshooting............................................................................................................................................ 49
Mobile Terminal is Totally Dead ............................................................................................................50
Flash Programming Does Not Work .....................................................................................................51
Power Does Not Stay on or the Mobile Terminal is Jammed ........................................................53
Charger Faults ............................................................................................................................................55
Audio Faults ................................................................................................................................................56
Earpiece .................................................................................................................................................... 56
Microphone ............................................................................................................................................. 57
IHF.............................................................................................................................................................. 58
Vibra .......................................................................................................................................................... 59
Display Faults ..............................................................................................................................................60
Main Display............................................................................................................................................ 60
Secondary Display.................................................................................................................................. 62
Keypad Faults .............................................................................................................................................63
Power Key ................................................................................................................................................ 63
UI Modules............................................................................................................................................... 64
EL Panel and Driver ............................................................................................................................... 65
USB ................................................................................................................................................................66
MMC ..............................................................................................................................................................70
FM Radio ......................................................................................................................................................71
Camera .........................................................................................................................................................73
Bluetooth .....................................................................................................................................................73
SIM ................................................................................................................................................................73
GPS ................................................................................................................................................................75

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Introduction
The 6255/6255i/6256/6256i baseband module is a tri-mode, Code Division Multiple
Access (CDMA), dual-band engine and is based on the DCT4.5 standard. The baseband
engine includes two major Application Specific Integrated Circuits (ASICs):
• D2200 — Universal Energy Management Enhanced Integrated Circuit (UEME IC),
which includes the audio circuits, charge control, and voltage regulators
• D2800 — Main phone processor, which includes system logic for CDMA, two
Digital Signal Processors (DSPs), the Main Control Unit (MCU), and the memory
The BL-6C Li-ion battery is used as the main power source and has a nominal capacity of
1070 mA/h.

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Figure 1: Baseband block diagram
PWM
Parallel
Battery Zocus
Sim MMC
Tiku EDGE
MCU ARM925
PDRAM
C-DSP Lead3
A-DSP Lead 3
2G System Logic
UEME
Regulation
Charge Control
Audio
FBUS / MBUS
SIM I/F
RTC
Tomahawk
DC Jack
Int Display
Production
Test IF
RF
Keyboard
Mic
IHF Speaker
Disp BL’s
Camera
IRDA
Bluetooth
FM Radio
Antenna
SMPS
SDRAM
CBUS
Nut
USB
PCM / UART
VCORE
VIO
Regulator
Serial
Ext Display
UHS Jack
EL
Amplifier
EarPiece
Vibra
Cam Flash
PWM
Flash Memory
(Program,
NOR)
Flash Memory
(User, NAND)
D
B
U
S
32 KHz
GPS
19.2 MHz
UART

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Power Up and Reset
The UEME ASIC controls the power up and resets. The baseband can be powered up in
the following ways:
• Pressing the Power button, which means grounding the PWRONX pin of the
UEME
• Connecting the charger to the charger input
• Initiating the Real-time Clock (RTC) alarm, when the RTC logic has been
programmed to give an alarm
After receiving one of the above signals (see Figure 2), the UEME counts a 20ms delay
and then enters reset mode. The watchdog and VCORE start, and if the battery voltage
(VBAT) is greater than Vcoff+, a 200ms delay is started to allow references to settle.
After this delay elapses, the VFLASH1 regulator is enabled. Then, 500us later, VR3, VANA,
and VIO are enabled. Finally, the Power Up Reset (PURX) line is held low for 20ms. This
reset (PURX) is fed to the baseband D2800 processor ASIC, which in turn generates resets
for the MCU and the DSP. During this reset phase, the UEME forces the Voltage
Controlled Temperature Controlled Oscillator (VCTCXO) regulator on regardless of the
status of the sleep control input signal to the UEME.
The FLSRSTx from the UEME is used to reset the flash during power up and to put the
flash in power down during sleep mode. All baseband regulators are switched on when
the UEME is powered on.
The UEME internal watchdogs are running during the UEME reset state, with the longest
watchdog time selected. If the watchdog expires, the UEME returns to the power off
state. The UEME watchdogs are internally acknowledged at the rising edge of the PURX
signal to always give the same watchdog response time to the MCU.
The following timing diagram represents the UEME start-up sequence from reset to
power-on mode.

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Figure 2: Power-on sequence and timing
Reference signal
PwrOnX
Charger Detection
RTC
UEMRSTX
VCORE
VFlash1
VIO
VANA
VR3
19.2MHz Clk
PURX
t1 t2 t4t3
Sleep Clock
t1 = 20ms
t2 = 200ms
t3 = 500us
t4 = 20ms
Reset mode is entered and
the watchdog starts
End of settling time (only if Vbat > Vcoff+_);
VFLASH1 regulator enabled
VR3, VANA, VIO, and VCORE enabled;
PURX held LOW
D2800 processor, MCU, and DSP are
reset; VCTCXO regulator forced on

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Figure 3: Measured power-on sequence and timing
Power Up - Power Key
When the power key is pressed, the UEME enters the power-up sequence. Pressing the
power key grounds the PWRONX pin on the UEME. The UEME PWRONX signal is not part
of the keypad matrix. The power key is only connected to the UEME. When the power key
is pressed, an interrupt is generated to the D2800 processor that starts the MCU. The
MCU then reads the UEME interrupt register through the UEME control bus (CBUS) and
notices that it is a PWRONX interrupt. If the PWRONX signal stays low for a certain time,
the MCU accepts this as a valid power-on state and continues with the SW initialization
of the baseband. If the power key does not indicate a valid power-on situation, the MCU
powers off the baseband.
Power Up - Charger Connection
In order to be able to detect and start charging in cases where the main battery is fully
discharged (empty), charging is controlled by start-up charging circuitry.
The VBAT voltage level is monitored by the Charge Control Block (CHACON) inside the
UEME. When the VBAT level is detected to be below the master reset threshold (VMSTR-),
charging starts. Connecting a charger forces the Charging Voltage (VCHAR) input to rise
above the charger detection threshold (VCHDET+). This causes the UEME to generate

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100mA of constant output current from the connected charger’s output voltage. The
battery’s voltage rises at it charges, and when the VBAT voltage level is detected to be
higher than master reset threshold limit (VMSTR+), the start-up charge is terminated.
When VBAT is greater than VMSTR+, the Master Output Reset (MSTRX) signal, which is
internal to the UEME, is set to a Logic 1. This causes the UEME RESET block to enter into
its reset sequence.
If the VBAT is detected to fall below VMSTR- during start-up charging, charging is
cancelled. Charging is restarted when a new rising edge on the VCHAR input is detected
(VCHAR rising above VCHDET+).
Power Up - RTC Alarm
If the mobile terminal is in power-off mode when the RTC alarm activates, a wake-up
procedure occurs. After the baseband is powered on, an interrupt is given to the MCU.
When the RTC alarm occurs during active mode, an interrupt is generated to the MCU.
Power Off
The baseband switches to power-off mode if any of following occurs:
• Power key is pressed
• Battery voltage is too low (VBATT < 3.2V)
• Watchdog timer register expires
The UEME controls the power-down procedure.
Power Consumption and Operation Modes
Power-off Mode
During power-off mode, the power (VBAT) is supplied to the D2800 processor, UEME,
MMC, vibra, LED, PA, and PA drivers. During power-off mode, the UEME leakage current
consumption is approximately 40uA + 15uA from ZOCOS.
Table 1: Power-up Sequence through Charger Detection
Condition Result
VBAT < VMSTR- (start-up charging) Charging starts (VCHAR level begins to rise)
VBAT < VMSTR- (during charging) Charging is cancelled. A new rising edge of VCHAR
(VCHAR > VCHDET+) is required to restart charging
VCHAR > VCHDET+ Battery charges (VCHAR is rising)
VBAT > VMSTR+ Charging ends. MSTRX is set high and the UEME resets.

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Sleep Mode
When the SLEEPX signal is detected low by the UEME, the mobile terminal enters sleep
mode. In sleep mode, both processors (MCU and DSP) are in stand-by mode. The mobile
terminal enters sleep mode only when both processors make this request. The following
processes occur during sleep mode:
• VIO and VFLASH1 regulators are put into low quiescent current mode
• VCORE enters LDO mode
• VANA and VFLASH2 regulators are disabled
• All RF regulators are disabled
• VCTCXO (19.2MHz clock) is shut down
• 32kHz sleep clock oscillator is used as the baseband reference clock
The average current consumption of the mobile terminal in this mode can vary
depending on the software state (e.g., slot cycle 0,1, or 2, and if the mobile terminal is
working on IS95 or IS2000 for CDMA). However, on average the current consumption is
about 1.3mA in sleep mode and 100mA in active mode.
Sleep mode is exited either by the expiration of a sleep clock counter in the UEME or by
some external interrupt (e.g., charger connection, key press, headset connection). Any of
these conditions cause a high SLEEPX signal, which is detected by the UEME, and causes
the mobile terminal to enter active mode where all functions are activated.
Active Mode
During active mode, the mobile terminal is in normal operation, scanning for channels,
listening to a base station, transmitting and processing information. There are several
sub-states in the active mode depending on the mobile terminal present state of the
mobile terminal, such as burst reception, burst transmission, if the DSP is working, etc.
In active mode, software controls the UEME radio frequency (RF) regulators (VR1A and
VR1B), which can be enabled or disabled. These regulators work via the UEME charge
pump. VSIM can be enabled or disabled, and its output voltage can be programmed to be
1.8V or 3.0V. VR2 and VR4—VR7 can be enabled, disabled, or forced into low quiescent
current mode. VR3 is always enabled in active mode, disabled during sleep mode, and
cannot be controlled by the software in the same way as the other regulators. VR3 only
turns off if both processors (DSP and MCU) request to be in sleep mode.
Charging Mode
Charging mode can be performed in parallel with any other operating mode. A BSI
resistor inside the battery indicates the battery type and size and corresponds to a
specific battery capacity.
The battery voltage, temperature, size, and charging current are measured by the UEME
and controlled by the Energy Management (EM) charging algorithm.

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The charging control circuitry (CHACON) inside the UEME controls the charging current
delivered from the charger to the battery. The battery voltage rise is limited by turning
the UEME switch off when the battery voltage has reached 4.2V. The charging current is
monitored by measuring the voltage drop across a 220mOhm resistor.
Power Distribution
In normal operation, the baseband is powered from the mobile terminal‘s battery. The
battery consists of one Lithium-Ion cell capacity of 1070 mAh and some safety and
protection circuits to prevent harm to the battery.
The UEME ASIC controls the power distribution to the entire mobile terminal through the
BB and RF regulators. The battery feeds power directly to the following parts of the
system:
•UEME
•PA
•Vibra
• Display lights
• Keyboard lights
The heart of the power distribution to the mobile terminal is the UEME. The UEME
includes all the voltage regulators and feeds the power to the system. The UEME handles
hardware power-up functions so the regulators are not powered and the power-up reset
(PURX) is not released if the battery voltage is less than 2.8V.
The baseband is powered from five different UEME regulators (see Table 2):
Table 2: Baseband Regulators
Regulator Maximum
Current (mA) Vout (V) Notes
VCORE
DC/DC
300 1.35 The power-up default value is 1.35V. The output voltage is
selectable: 1.0V/1.3V/1.5V/1.8V.
(Note: If using D2800 processor version 1, the default is
1.57V.)
VIO 150 1.8 Enabled always except during power-off mode
VFLASH1 70 2.78 Enabled always except during power-off mode
VFLASH2 40 2.78 Enabled only when data cable is connected
VANA 80 2.78 Enabled only when the system is awake (off during sleep and
power-off modes)
VSIM 25 3.0 Enabled during power-up mode and scanning for a SIM card

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Table 3 includes the UEME RF regulators.
The charge pump that is used by VR1A is constructed around the UEME. The charge
pump works with the 1.2MHz clock (CBUS) oscillator and gives a 4.75V regulated output
voltage to the RF.
Table 3: RF Regulators
Regulator Maximum
Current (mA) Vout (V) Notes
VR1A 10 4.75 Enabled when cell receiver is on
VR1B 10 4.75 Enabled when the transmitter is on
VR2 100 2.78 Enabled when the transmitter is on
VR3 20 2.78 Enabled when SleepX is high
VR4 50 2.78 Enabled when the receiver is on
VR5 50 2.78 Enabled when the receiver is on
VR6 50 2.78 Enabled when the transmitter is on
VR7 45 2.78 Enabled when the receiver is on

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Clock Distribution
RFClk (19.2MHz Analog)
The main clock signal for the baseband is generated from the voltage-controlled
temperature-controlled crystal oscillator (VCTCXO). This 19.2MHz clock signal is
generated by the radio frequency circuitry and fed to the radio frequency clock (RFCLK)
pin of the D2800 processor. The 19.2MHz clock can be stopped during sleep mode by
disabling the UEME regulator output (VR3), which in turn powers off the VCTCXO.
Figure 4: Waveform of the 19.2MHz clock (VCTCXO)

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RFConvClk (19.2MHz Digital)
The D2800 processor distributes the 19.2MHz clock to the internal processors (the DSP
and MCU) where the software multiplies this clock by seven (=134.4MHz) for the DSP
and by two (=38.4MHz) for the MCU.
Figure 5: RFCovCLk waveform

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CBUSClk Interface
CBUS utilizes a 1.2MHz clock signal, which is used by the MCU to transfer data between
the UEME and the D2800 processor.
Figure 6: CBUS data transfer

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DBUS Clk Interface
DBUS utilizes a 9.6MHz clock signal, which is used by the DSP to transfer data between
the UEME and the D2800 processor.
Figure 7: DBUS data transfer

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SleepCLK (Digital)
The UEME provides a 32kHz sleep clock for internal use and also to the D2800 processor,
where it is used for the sleep-mode timing.
Figure 8: 32 kHz Digital output from UEME

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SleepCLK (Analog)
When the system enters sleep mode or power-off mode, the external 32KHz crystal
provides a reference to the UEME. The RTC circuit also uses this clock to turn on the
mobile terminal during power-off or sleep mode.
Figure 9: 32KHz analog waveform at 32KHz crystal input
Flash Programming
Connections to Baseband
The flash programming equipment is connected to the baseband using test pads for
galvanic connection. The test pads are allocated in such a way that they can be accessed
when the mobile terminal is already assembled. The flash programming interface
includes the VPP, FBUSTX, FBUSRX, MBUS, and BSI signals, which are used by the FLS-8
for flashing. The connection is through the UEME, which means that the logic voltage
levels of these signals correspond to 2.78V. Power is supplied to the mobile terminal
using the battery contacts.
Baseband Power Up
The baseband power is controlled by the flash prommer in production and in
re-programming situations. The baseband powers up by applying supply voltage to the
battery terminals. After the baseband is powered up, flash programming indication
begins (see the following "Flash Programming Indication" section).

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Flash Programming Indication
After connecting the flash prommer to the mobile terminal, the flash prommer sets the
MBUS line low to notify the MCU that the flash prommer is connected. This causes the
UEME reset state machine to perform a reset to the system by setting the PURX signal
low for 20ms.
During flash programming, the MBUS signal transmitted from the UEME to the flash
prommer is used as the clock for synchronous communication. This MBUS clock is also
supplied by the UEME to the D2800 processor, along with the MBUSRX signal. If the
MBUSRX signal is low, the MCU enters flash programming mode. To avoid accidental
entry into flash-programming mode, the MCU waits to get input data from the flash
prommer. If the timer expires without any data being received, the MCU continues the
boot sequence.
When the mobile terminal has entered flash programming mode, the flash prommer
writes an 8-bit password to the UEME to indicate that flash programming/
reprogramming is to take place. This 8-bit data is transmitted through the FBUSRX line
into a shift register inside the UEME. When the 8 bits have been shifted into the register,
the flash prommer generates a falling edge on the BSI line. This loads the shift register
content into a comparison register inside the UEME. If the 8 bits in the comparison
register matches the default value preset in the UEME, programming starts.
In order to avoid spurious loading of the register, the BSI signal is gated during UEME
master reset and during power up when the PURX is active (low). The BSI signal must not
change states during normal operation unless the battery is extracted. If the battery is
extracted, the BSI signal is pulled high.
Note: A falling edge is required to load the comparison register.
The UEME flash programming mode is valid until the MCU sets a bit in the UEME register
that indicates the end of flash programming. Setting this bit also clears the comparison
register in the UEME previously loaded at the falling edge of the BSI signal. During the
flash programming mode, the UEME watchdogs are disabled. Setting the bit indicating
the end of flash programming enables and resets the UEME watchdog timer to its default
value. Clearing the flash programming bit also causes the UEME to generate a reset to
the D2800 processor.
Flashing
Flash programming is done through the VPP, FBUSTX, FBUSRX, MBUS, and BSI signals.
When the mobile terminal enters flash programming mode, the prommer indicates that
flash programming will take place by writing an 8-bit password to the UEME. The
prommer sets the BSI value to “1” and then uses FBUSRX for writing and MBUS for
clocking. The BSI is then set back to “0”.
The MCU uses the FBUSTX signal to indicates to the prommer that it has been noticed.
After this, the MCU reports the ID type to the D2800 processor and is ready to receive
the secondary boot code to its internal SRAM.