Keypad Switches And Scanning - LG C1100 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 24 switches (SW1-SW2,KB2~KB22),
connected in a matrix of 5 rows by 5 columns, as shown in Figure, except for the power switch
(KB101), which is connected independently. Functions, the row and column lines of the keypad
are connected to ports of AD6525. 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 AD6525
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
SW1 SW2
UP
4 1 4 1
5 3 2 5 3 2
VA201 VA202
R242 R243
680
680
KB4
1
SP204 SP205
KB5
4
SP211 SP212
KB6
7
SP227 SP228
KB7
*
SP231 SP232
Figure 3-24. C1100 KEYPAD CIRCUIT
- 35 -
3. TECHNICAL BRIEF
KEYON (AD6537B)
C144
0.01u
DOWN
KB20 KB16
2 3
SP206 SP207
KB21 KB17
5 6
SP209 SP210
KB2 KB18
8 9
SP229 SP230
KB3 KB19
0 #
SP233 SP234
PWR KEY
R161
KB101
1K
KB22
CLR
SP201
KB9 KB8
LEFT MENU
SP208
KB10 KB13
UP SELECT
SP213
KB11 KB14
RIGHT SEND
SP226
KB12 KB15
DOWN CONFIRM
SP235