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3. TECHNICAL BRIEF
3.8 Keypad Switches and Scanning
The key switches are metal domes, which make contact between two concentric pads on the keypad
layer of the PCB when pressed. There are 26 switches (Normal Key 24EA, Volume up down side key,
PWR down side key), connected in a matrix of 5 rows by 5 columns, as shown in Figure 3-11, except
for the power switch (SW301), which is connected independently. Functions, the row and column lines
of the keypad are connected to ports of AD6720. The columns are outputs, while the rows are inputs
and have pull-up resistors built in. When a key is pressed, the corresponding row and column are
connected together, causing the row input to go low and generate an interrupt. The columns/rows are
then scanned by AD6720 to identify the pressed key.
R308
10K
R309
680
POWERKEY
KEY_ROW0
KEY_ROW1
KEY_ROW2
KEY_ROW3
KEY_ROW4
KEY_COL0
KEY_COL1
KEY_COL2
KEY_COL3
KEY_COL4
VBAT
SW301
END
R319
680
R322
680
EVL14K02200
R327
680
EVL14K02200
R330
680
EVL14K02200
R334
680
VA309
EVL14K02200
R336
680
R337
680
R338
680
R339
680
R340
680
Figure 3.8 Keypad Switches and Scanning
VOL_UP
SW300
CN300
T
R315
R316
100ohm
100ohm
SW304
SW305
1
2
SW309
SW310
VA306
4
5
VA307
SW314
SW315
7
8
VA308
SW319
SW320
*
0
- 32 -
VOL_DOWN
SW302
SW303
CLR
FAV
SW306
SW307
3
LEFT
SW311
SW312
6
UP
SW316
SW317
9
RIGHT
SW321
SW322
#
DOWN
SW308
MENU
SW313
SEL
SW318
SEND
SW323
CONF
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