Only For Training And Service Purposes - LG GM210 Service Manual

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.
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Copyright © 2009 LG Electronics. Inc. All right reserved.

Only for training and service purposes

Figure 3-12-2 keypad interface and interrupt generation logic
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
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3. TECHNICAL BRIEF
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