Voxtel W420, Руководство по ремонту

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The interference created in these devices amounts to AM demodulation.
The RACH burst can be heard as a single 'Tick' sound. It's quickly followed by the SDCCH 'Tat, Tat-tattat,
tat-tat-tat ...'. After a few seconds, the TCH is connected 'Buzzzzzzzzz'.
Mobile Handoff
We have covered mobile power on and call establishment, but there is one other important area. During
a call the mobile may have to change base stations. If the call is between faces of the same base station, this
is performed locally. The case shown here is that where the base station is not the same. The mobile reports
its measurements and the serving BSC determines that it is time to perform a handoff. It will contact the new
base station and get the information on the new channel and timeslot (along with midamble and timing
information) and send this to the mobile. It then commends the mobile to switch base stations and then once
the new call is established, close down the old link and reallocate it to another user if necessary.
6. Summary introduction of mostly chips used in W420
Chips used in W420 can be divided into flat and application manage according to function. There is the
introduction of these two chips
6.1
：
Flat Chip
：
U201
：
DBB
——
Digital Base Band , composed of ARM7 TDMIE CPU and TMS320C54X DSP dual inter
core. The chip integrate 4Mbit Memory inside
、
provide multi control interface outside. There is the basic
structure as follows:
Figure6.1: DBB basic structure
Main structure characteristic and function of DBB (Part Number is D751992AGHHR ) including:
Nuclear working voltage 1.5V (1.35-1.65V ), IO voltage 2.8V( 2.5V-3V )
Working temperature range -40~ +85
℃
CPU working at 52MHz, DSP working at 104MHz
Integrate 4Mbit SPAM Memory inside
289 pin uStarBGA encapsulation