Keypad Switches And Scanning - LG MG120a Service Manual

3. TECHNICAL BRIEF

3.3.5 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 21 switches, connected in a matrix
of 5 rows by 5 columns and additional GPIO 35 for KEY_ROW5, as shown in Figure 3-8,
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.
KEYPADON
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