Keypad/Passport Option Board; Figure 3-1. Dc Power Distribution Block Diagram; Figure 3-2. Keypad/Passport Option Board Block Diagram - Motorola HT1250-LS+ Service Manual

3-2
.
UNSWB+
7.5V
Battery
Fuse
MECH.
SWB+
3.3V
Reg.
LI Ion
PA, Driver
PCIC(ALC)
3.3

Keypad/PassPort Option Board

The keypad/PassPort Option Board block diagram is shown in Figure 3-2. The keypad circuitry is
contained on the PassPort Option Board.
Two resistive voltage divider networks form a row and column matrix. Pressing any button
simultaneously grounds a tap on the row and column voltage dividers which outputs a unique row
voltage and column voltage level for that button location. The row and column voltages are applied to
two A/D inputs of the microprocessor (U409 pins 60 and 61). The keypad column voltage is also
applied to a comparator whose threshold is set to produce an interrupt signal (KEY_INT) whenever
any key is pressed. The microprocessor then samples the voltage levels at the keypad row and
keypad column A/D inputs and makes a comparison with a map table to identify the key pressed.
Once the key is identified, a corresponding function is executed.
The LED_EN is set by the codeplug. When the value is set to low, the LED lights up during power up.
A high codeplug setting disables this feature.
Display
Audio
Power
Amplifier
SWB+
Control
On/Off
Switch
Low Battery
Detect
Antenna
Switch

Figure 3-1. DC Power Distribution Block Diagram

18 Pin
Connector

Figure 3-2. Keypad/PassPort Option Board Block Diagram

Vdda
Vdda
Regulator
Vddd
Vddd
Regulator
MCU, ROM
Tx
and EEPROM
Led
5V
Regulator
5V
Data
40 Pin Connector
Key_Int
Comparator
LED
Theory of Operation
Accessories
20 pin Connector
Keypad/Option Board
LCD
FRACTN
ASFIC_CMP
Driver
VCOBIC
RF AMP, IF AMP,
RX/TX Buffers
IFIC
Keypad Column
Keypad
Row
Keypad
Button