Circuit Description - Samsung SCH-3500 series Service Manual

6. Circuit Description

6-1 Logic Section
6-1-1 Power Supply
With the battery installed on the phone and by
pressing the PWR key, the VBATT and ON_SW
signals will be connected. This will turn on Q905
(2SC4081BR). This in turn will be supplied to
regulators (U905 and U907), thus releasing them
from the shut-down state to output regulated 3.0V.
The VBATT applied to ON_SW will turn on Q907
(DTC144EE) resulting in the signal ON_SW_SENSE
to change state from HIGH to LOW. This will allow
MSM to send out PS_HOLD (logical HIGH) to turn
on Q905 even after the PWR key is released.
The voltage (+3.0VD) from U907 is used in the
digital parts of MSM. The voltage (+3.0VA) from
U905 is used in the analog part.
6-1-2 Logic Part
The Logic part consists of internal CPU of MSM,
Memory and EEPROM. The MSM receives TCXO
and CHIPX8 clock signals from the IFR and controls
the phone during the CDMA and the FM mode. The
major components are as follows:
•CPU : ARM7TDMI Micro-processor
•Memory : U801 (MB84VD21194-85-PBS)
16M Flash ROM, 4M SRAM
•EEPROM : U903 (M24256)
256K Serial EEPROM
SAMSUNG Proprietary-Contents may change without notice
CPU
ARM7TDMI microprocessor is used for the main
processing. The CPU controls all the circuitry. For
the CPU clock, 27 MHz resonator is used.
MEMORY (U801)
16M Flash and 4 M SRAM one package is used to
store the terminals programs , the internal flag
information, call processing data, and timer data.
Using the down-loading program, the program can
be changed even after the terminal is fully
assembled.
EEPROM (U903)
One 256 kbit EEPROM is used to store ESN, NAM,
power level, volume level, and telephone number.
KEYPAD
For key recognition, key matrix is setup using
SCAN0-6 of STORE signals and KEY0-3 of input
ports of MSM. Ten LEDs and backlight circuitry are
included in the keypad for easy operation in the
dark.
LCD MODULE
LCD module contains a controller which will
display the information onto the LCD by 8-bit data
from the MSM.
6-1