Keypad Switches And Scanning - LG KP260 Service Manual

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 25 switches (Normal Key 22EA, Volume up down and
camera side key, connected in a matrix of 5 rows by 5 columns, as shown in Figure 3-8, except for the
power switch (END), which is connected independently. Functions, the row and column lines of the
keypad are connected to ports of AD6726. 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 AD6726 to identify the pressed key.
KEY_ROW0
KEY_ROW1
KEY_ROW2
KEY_ROW3
KEY_ROW4
KEY_COL0
KEY_COL1
KEY_COL2
KEY_COL3
KEY_COL4
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
R209 680
4 R211 680
3 R215 680
2 VA204
VA202
1
CN202
varistor
varistor
R216 680
KEY200
1
R218 680
VA209
KEY203
4
R223 680
VA210
KEY206
7
R225 680
VA211
STAR
*
R226 680
VA212
R227 680
R228 680
R229 680
Figure 3.8 Keypad Switches and Scanning
3. TECHNICAL BRIEF
R210
R212
VA205 VA206 VA203
varistor varistor varistor
KEY201 KEY202
2 3
KEY204 KEY205
5 6
KEY207 KEY208
8 9
KEY209 SHARP
0 #
- 33 -
680
680
3
2
1
CN201
UKEY_ROW0
UKEY_ROW1
UKEY_ROW2
UKEY_ROW3
UKEY_ROW4
KEY_COL3
KEY_COL4
LGE Internal Use Only