Power Up And Reset - Nokia 6255 Description And Troubleshooting

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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.
Issue 2 05/2005
©2005 Nokia Corporation
6255/6255i6256/6256i (RM-19)
Baseband Description and Troubleshooting
Company Confidential Page 7