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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),
connected in a matrix of 5 rows by 5 columns and additional GPIO 35 for KEY_ROW5, as shown in
Figure 3-11, except for the power switch (KB1), 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.
POWERKEY
R301
680
KEY_ROW0
KEY_ROW1
KEY_ROW2
KEY_ROW3
KEY_ROW4
KEY_COL0
KEY_COL1
KEY_COL2
KEY_COL3
KEY_COL4
VBAT
R300
END
10K
SW304
R302
100
R320
680
R324
680
VA306
EVL14K02200
R326
680
VA307
EVL14K02200
R331
680
R336
680
R339
680
R341
680
R342
680
R343
680
R344
680
Figure 3-11. Keypad Switches and Scanning
VOL_UP
VOL_DOWN
SW300
T
R303
100
1
2
SW307
SW308
SW309
SW312
SW313
SW314
4
5
SW317
SW318
SW319
7
8
SW322
*
SW323
0
SW324
- 30 -
CLR
FAV
SW305
SW306
3
LEFT
SW310
SW311
MENU
SW315
SW316
6
UP
SEL
SW320
SW321
9
RIGHT
SEND
#
SW325
SW326
DOWN
CONF
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