Theory of Operation
Introduction/Theory of Operation B.1-3
2.6 Keypad and Top Keys
The HHCH keypad has 22 keys, plus 3 additional top keys, the on/off key being one of them, which
are located on the top of the HHCH.
All keys of the keypad are configured as 2 analogue lines (ANALOG_1 & ANALOG_2) to the radio.
The microprocessor in the mobile radio will compare the voltage when any one of the keypad row or
keypad column keys is being pressed. The microprocessor will then sample the Analog to Digital
voltages at the keypad row and keypad column and map it with the table (shown as below) 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.
Normally, the ANALOG_1 and ANALOG_2 is 5V (without pressing any key)
The three top keys are configured to ANALOG_3 to the radio. The voltage on the analogue lines
depends on which key is pressed. (0V for ON/OFF Button, 1.31V for EMG Button and 2.55V for CLR
Button).
The voltages of these lines (ANALOG _1, 2 & 3) are A/D converted inside the microprocessor on the
mobile radio and are used to specify the pressed button.
2.7 Status LED and Back Light Circuit
All the indicator LEDs (2) and the back light LEDs (18) are driven by current sources Q0982 –
Q0985 and controlled by the microprocessor in mobile radio via SERIAL PERIPHERAL INTERFACE
(SPI). Shift Register U0983 stores the LED status. To update the LED status line LED CLCK BUF
shifts the data of line SPI DATA BUF into the Shift Register. When all the data has been written, line
LED CD is set to low for a few microseconds to update the output of the Shift Register with the new
data.
ANALOG_2 /V
ANALOG_1 /V
(C1)
0
(C2)
1.21
(C3)
2.31
(C4)
3.29
(C5)
4.18
(R1)
0
S13
(EDIT)
S14
(Alarm)
S15
(RD)
(R2)
1.21
S21
(<OPT)
S22
(S)
S23
(Phone)
S24
(Vol ^)
S25
(Mode ^)
(R3)
2.31
S31
(1)
S32
(2)
S33
(3)
S34
(Vol
∨
)
S35
(Mode
∨
)
(R4)
3.29
S41
(4)
S42
(5)
S43
(6)
S44
(8)
S45
(9)
(R5)
4.18
S51
(7)
S52
(*)
S53
(0)
S54
(#)
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