LG B2100, Service Manual

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Service Manual /
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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 22 switches (Normal Key 21EA, Camera side key), connected in a
matrix of 5 rows by 5 columns and additional GPIO 35 for KEY_ROW5, as shown in Figure 3-24, except for
the power switch (KB1), which is connected independently. Functions, the row and column lines of the
keypad are connected to ports of AD6527. 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 AD6527 to identify the pressed
key.
Figure 3-27. Keypad Switches and Scanning