LG KG280 Service Manual - Page 31

Keypad Switches and Scanning

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3. TECHNICAL BRIEF 3.9 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 14 switches (Normal Key 12EA, Volume up down side key, PWRdown side key), connected in a matrix of 5 rows by 3 columns, as shown in Figure 3-11, 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. KEY KEY_ROW0 KEY_ROW1 KEY_ROW2 KEY_ROW3 KEY_ROW4 KEY_COL0 KEY_COL1 KEY_COL2 SIDE KEY NUMERIC KEY MATRIX VOLUME UP DN CN400 SW400 1 SW401 2 SW402 3 4 3 2 1 5 4 3 2 1 END CAM CN401 VBAT R401 10K VA403 R402 680 SW403 SW404 SW405 PG05DBTFC 4 SW406 5 SW407 6 SW408 * VA403 : NA 7 SW409 * 8 SW410 0 9 SW411 # POWERKEY VA400 PG05DBTFC VA401 PG05DBTFC VA402 PG05DBTFC Figure 3-11. Keypad Switches and Scanning LGE Internal Use Only - 32 - Copyright © 2007 LG Electronics. Inc. All right reserved. Only for training and service purposes

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- 32 -
3. TECHNICAL BRIEF
3.9 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 14 switches (Normal Key 12EA, Volume up down side key,
PWRdown side key), connected in a matrix of 5 rows by 3 columns, as shown in Figure 3-11, 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.
LGE Internal Use Only
Copyright © 2007 LG Electronics. Inc.
All right reserved.
Only for training and service purposes
KEY
NUMERIC KEY MATRIX
6
0
* VA403 : NA
*
#
5
DN
9
SIDE KEY
END
1
7
UP
VOLUME
4
3
CAM
8
2
SW403
SW400
SW409
2
3
4
5
CN401
1
PG05DBTFC
VA400
VA403
PG05DBTFC
SW407
SW406
SW410
SW401
SW402
CN400
1
2
3
4
SW408
SW411
PG05DBTFC
VA402
VA401
PG05DBTFC
R401
10K
VBAT
SW405
SW404
680
R402
KEY_ROW0
KEY_COL2
KEY_ROW1
KEY_ROW2
KEY_ROW3
KEY_ROW4
KEY_COL1
KEY_COL0
POWERKEY
Figure 3-11. Keypad Switches and Scanning