ADP5588
THEORY OF OPERATION
REF
ADP5588
GND
VOLTAGE
19
21
23
22
20
24
V
CC
V
CC
V
CC
C9
C8
SCL
SDA
18
17
C9
C8
C9
C8
0.1µF
CONTROL
REGISTERS
CONTROL
INTERFACE
REF
VOLTAGE
RST
INT
0.1µF
SCL
SDA
RST
INT
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
A7 A6 A5 A4 A3 A2 A1 A0
B7 B6 B5 B4 B3 B2 B1 B0
C7 C6 C5 C4 C3 C2 C1 C0
D7 D6 D5 D4 D3 D2 D1 D0
E7 E6 E5 E4 E3 E2 E1 E0
F7 F6 F5 F4 F3 F2 F1 F0
G7 G6 G5 G4 G3 G2 G1 G0
H7 H6 H5 H4 H3 H2 H1 H0
I7 I6 I5 I4 I3 I2 I1 I0
J7 J6 J5 J4 J3 J2 J1 J0
Figure 4. Typical Operating Circuit
The ADP5588 is a GPIO expander that can be configured either
as an 18-I/O port expander or as a 10 column × 8 row keypad
matrix (80 keys maximum). It is ideal for cellular phone designs
and other portable devices that require a large extended keypad
and/or expanded I/Os (see the Applications Information section
for various configurations). When smaller size keypads are
required, unused GPIOs in the keypad matrix can be used as
I/Os (GPOs and GPIs). Two of the columns (C8 and C9) can
also be configured as comparator inputs for single or dual light
sensors. All GPIOs (rows and columns) default as GPIs at power-
up with pull-ups and debounce enabled.
Table 10. Key Event Number Assignment Table
Row C0 C1 C2 C3 C4 C5 C6 C7 C8 C9
1
2
4
4
5
6
7
8
9
10
R0
R1
R2
R3
R4
R5
R6
R7
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
When one key press or multiple key presses (short between
coumn and row) occur, the internal state machine checks the
row pins to determine which one is driven low and then triggers
an interrupt. The state machine then starts a key scan cycle to
determine which keys are pressed. After a key has been pressed
for 25 ms, the state machine sets the appropriate key(s) in the
key event status register with the key-pressed bits set (the MSB
in the key event register) in the order detected. If the KE_IEN
field in Register 0x01 is set, the state machine then sets the
KE_INT field in Register 0x01 and generates an interrupt to the
host processor.
KEYPAD OPERATION
Any number of rows and columns, up to 10 columns × 8 rows,
can be configured to be part of the keypad matrix. The rows
and columns that make up the keypad matrix must be con-
figured by setting the corresponding bits in Register 0x1D
through Register 0x1F. Keys on the keypad matrix appear on
the key event table with a decimal value of 1 (0x01 hexidecimal
or 0000001 binary) and run through 80 decimals (0x50 hexi-
decimal or 1010000 binary). See Table 10 for key event number
assignments. The keypad, in idle mode, is configured with
columns being driven low and rows as inputs high with pull-
ups.
Rev. A | Page 7 of 28
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