Samsung SCH-1900, Service Manual, Page: 11 / 112

Samsung Electronics 4-1
4. Circuit Description
4-1 Logic Section
4-1-1 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
Q108(2SC4081). This in turn will be supplied to
pin 6 of regulators U110 and U111, thus releasing
them from the shut-down state to output
regulated 3.3V. And then the pin 8 of (U110) stays
High.
The VBATT applied to ON_SW turns on
Q113(DTC144) and will result in the signal
ON_SW_SENSE to change state from HIGH to
LOW. The MSM recognizes this signal and sends
out PS_HOLD(logical HIGH) to turn on
Q108 even after the PWR key is released.
The power from U110 is used in the digital part of
MSM and BBA. The power from U111 is used in
the analog part of BBA.
4-1-2 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. The major components are
as follows:
¶U
CPU : INTEL 80186 core
¶U
FROM : U112 (MBM29LV800T)-8MBIT
FLASH ROM
¶U
SRAM : U113(KM68V2000BLTI)-2MBIT
STATIC RAM
¶U
EEPROM : U109(24LC65-1/SM)-64KBIT
SERIAL EEPROM
CPU
INTEL 80186 CMOS type 16-bit microprocessor is
used and CPU controls all the circuitry. For the
CPU clock, 27MHz is used.
FLASH ROM
One 8Mbit 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 2Mbit SRAM is used to store the internal flag
information, call processing data, and time data.
EEPROM
One 64Kbit EEPROM is used to store ESN, NAM,
power level, volume level, and telephone number.
KEY-PAD
For key recognition, key matrix is setup using
SCAN0-6 of STROBE signals and KEY0-2 of input
ports of MSM. Six 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 -3.3V for fine view angle and LCD
reflector to improve the display efficiency.