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3. TECHNICAL BRIEF
3.11 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 25switches (S301-S325), connected in a matrix
of 5 rows by 5 columns, as shown in Figure, except for the power switch (S310), which is connected
independently.
Functions, the row and column lines of the keypad are connected to ports of AD6522. 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 AD6522 to identify the pressed key.
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DOWN
Figure 3-11. Keypad Switches and Scanning.
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