ADP5588ACPZ-R7 datasheet(7/28 Pages) AD

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ADP5588

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THEORY OF OPERATION

CONTROL

REGISTERS

CONTROL

INTERFACE

REF

VOLTAGE

SCL

SDA

RST

INT

VCC

GND

VCC

SCL

SDA

VCC

REF

VOLTAGE

0.1µF

ADP5588

RST

INT

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

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.

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