Circuit Description - Samsung SCH-211 Service Manual

5. Circuit Description

5-1 Logic Section
5-1-1 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 Q102
(2SC4081BR) and will drive DC-DC converter
(U123) to output 5.0V. This in turn will be sup-
plied to pin 6 of regulators (U121 and U122), thus
releasing them from the shut-down state to output
regulated 3.3V.
The VBATT applied to ON_SW will turn on Q103
(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 Q102 even after the
PWR key is released.
The voltage (+3.3V) from U121 is used in the digi-
tal parts of MSM and BBA. The voltage (+3.3AV)
from U122 is used in the analog part of BBA. The
voltage from U124 (output of 5V) is used for the
audio circuitry.
5-1-2 Logic Part
The Logic part consists of internal CPU of MSM,
RAM, ROM and EEPROM. The MSM receives
TCXO and CHIPX8 clock signals from the BBA
and controls the phone during the CDMA and the
FM mode. The major components are as follows:
¥ CPU : INTEL 80186 core
¥ FROM : U126 (MBM29LV800T) - 8MBIT
FLASH ROM
¥ SRAM : U127 (KM68V2000I) - 2MBIT
STATIC RAM
¥ EEPROM : U113 (AT24C128) - 128KBIT SER-
IAL EEPROM
Samsung Electronics-Contents may change without notice.
CPU
INTEL 80186 CMOS type 16-bit microprocessor is
used for the main processing. The CPU controls
all the circuitry. For the CPU clock, 27MHz
resonator is used.
FLASH ROM
One 8 MBIT FROM is used to store the terminalÕs
program. Using the down-loading program, the
program can be changed even after the terminal is
fully assembled.
SRAM
One 2 MBIT SRAM is used to store the internal
flag information, call processing data, and timer
data.
EEPROM
One 128 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. Eight 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. It also consists a DC-DC
converter to supply -3.5V for fine view angle and
LCD reflector to improve the display efficiency.
5-1