MCP23008-ESLASHSS datasheet(21/44 Pages) MICROCHIP

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DS21919D-page 21

MCP23008/MCP23S08

1.7

Interrupt Logic

The interrupt output pin will activate if an internal

interrupt occurs. The interrupt block is configured by

the following registers:

• GPINTEN – enables the individual inputs

• DEFVAL – holds the values that are compared

against the associated input port values

• INTCON – controls if the input values are

compared against DEFVAL or the previous values

on the port

• IOCON (ODR and INPOL) – configures the INT

pin as push-pull, open-drain and active-level

Only pins configured as inputs can cause interrupts.

Pins configured as outputs have no affect on INT.

Interrupt activity on the port will cause the port value to

be captured and copied into INTCAP. The interrupt will

remain active until the INTCAP or GPIO register is

read. Writing to these registers will not affect the

interrupt.

The first interrupt event will cause the port contents to

be copied into the INTCAP register. Subsequent

interrupt conditions on the port will not cause an

interrupt to occur as long as the interrupt is not cleared

by a read of INTCAP or GPIO.

1.7.1

INTERRUPT CONDITIONS

There are two possible configurations to cause

interrupts (configured via INTCON):

Pins configured for interrupt-on-pin-change

will cause an interrupt to occur if a pin changes

to the opposite state. The default state is reset

after an interrupt occurs. For example, an

interrupt occurs by an input changing from 1 to

0. The new initial state for the pin is a logic 0.

Pins configured for interrupt-on-change from

the corresponding input pin differs from the

long as the condition exists, regardless if the

INTAP or GPIO is read.

See Figure 1-6 and Figure 1-7 for more information on

interrupt operations.

FIGURE 1-6:

INTERRUPT-ON-PIN-

CHANGE

FIGURE 1-7:

INTERRUPT-ON-CHANGE

FROM REGISTER

DEFAULT

GPx

INT

ACTIVE

Port value

is captured

into INTCAP

Read GPIU

or INTCAP

Port value

is captured

into INTCAP

INT

Port value

is captured

into INTCAP

Read GPIU

or INTCAP

DEFVAL

GP2

210

GP:

ACTIVE

(INT clears only if interrupt

condition does not exist.)

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