Datasheet

© 2007 Microchip Technology Inc. DS21919E-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):
1. 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.
2. Pins configured for interrupt-on-change from
register value will cause an interrupt to occur if
the corresponding input pin differs from the
register bit. The interrupt condition will remain as
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 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
X X X X X 0 X X
GP2
76543210GP:
ACTIVE
ACTIVE
(INT clears only if interrupt
condition does not exist.)