1-4 THEORY OF OPERATION
ModB/Vstby Supply
Under various conditions, the supply to the ModB/Vstby would vary. Table Table 1-1 shows these
conditions and circuits in operation.
3.3 Keypad (GPx88/R)
The LED_EN setting is set by the codeplug. When the value is set to high, the LED will not light up
during power up and vice versa.
U602 is a comparator that will compare the voltage when any one of the keypad row or keypad
column keys is being pressed. Therefore when a key is being pressed, it will send a message to the
microprocessor through the output (KEY_INT) telling it that a key has been pressed. The
microprocessor will then sample the Analog to Digital voltages at the keypad row and keypad
column and map it with the table so that the key being pressed can be identified. Once the key has
been identified, the message that corresponds to the key will show up at the display.
Table 1-1 ModB/Vstby Supply Modes
Condition Circuit Operation
Radio On Vdd supply voltage via CR411
Radio Off • Vdd turned off
• Q416 gate is pulled low by R462
• Q416 is switched on
• U410 supplies 3.2V to ModB/Vstby
Primary battery removed • Vdd turned off
• Q416 gate is pulled low by R462
• Q416 is switched on
• Li Ion battery provides 3.2V to ModB/Vstby
Flash Mode • Boot_Ctrl line pull low
• ModA & ModB goes low
• Processor in boot-strap mode
• Flashing enabled
Figure 1-4 Keypad Block Diagram
Micro Processor
Comparator
Keypad
Button
LED
Display
18 pin connector
Key_Int
Keypad Column
Keypad
Data
Row
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