Only For Training And Service Purposes - LG GM200 Service Manual

3. TECHNICAL BRIEF
The keypad interface supports a row/column decoding of a keyboard matrix of up to 8 rows and 8
columns. The interface generates an interrupt when any key is pressed, and the interrupt is routed
through the system interrupt controller to the MCU. Software must scan the columns to determine
which key was pressed. Debouncing must also be implemented in software. The keypad interface
consists of eight tristateable KEYPADCOL outputs and eight KEYPADROW inputs. Pressing a key pulls the
corresponding KEYPADROW input low. When all KEYPADCOL outputs are driven low, pulling any
KEYPADROW input low generates an interrupt.
In the interrupt service routine, the keypad must be scanned by setting only one column output low at a
time and reading the row inputs. A zero is read anywhere a key is pressed on that column. The scan
should be repeated at regular intervals until no key is being pressed. To implement debouncing, the
software must require the same scan result for several scans. The keypad interrupt should not be cleared
until no key has been pressed for several scans.
The 8 by 8 matrix of rows and columns provides the possibility of up to 64 keys (with an additional 8 if a
ghost column is used). Full flexibility in enabling and disabling individual rows and columns is provided.
Any rows or columns not used should be disabled in the Keypad Control Register. The following figure
shows the keypad interface and interrupt generation logic.
LGE Internal Use Only
LGE Internal Use Only
Figure 3-7-3 keypad interface and interrupt generation logic
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Only for training and service purposes