Samsung SCH-570, Service Manual

Page: 6 / 33

5-1
5. Circuit Description
5-1 Logic Section
5-1-1 Power Supply
With the battery installed on the phone and by
pressing the END/ key, the VBATT and
ON_SW signals will be connected. This will turn
on U123 DC_DC convertor.
This in turn will be supplied to PIN3, PIN4 of
regulators U124, PIN6 of regulators 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 the start from
High to Low.)
The MSM recognizes this signal and sends out
PS_HOLD (logical HIGH) to turn on Q102 even
after the PWR key is released.
The power from U124 is used in the digital part of
MSM and BBA. The power from U122 is used in
analog part of BBA.
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 operation. The
major components are as follows:
CPU : INTEL 80186 core (inside the MSM)
FLASH ROM : U701 - 8 Mbit FLASH MEMORY
SRAM
: U703 - 2 Mbit STATIC RAM
FLASH ROM : U702 - 1 Mbit FLASH MEMORY
EEPROM : U102 - 128 Kbit SERIAL EEPROM
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 terminal's
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 to set up using
SCAN0-6 of STORE signals and KEY0-3 of input
ports of MSM. Ten LEDs and backlighting
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.