Datasheet

and AD0 to V+ or GND (shown in bold in Table 3). These
selections are guaranteed to be correct at power-up,
independent of SDA and SCL behavior. If one of the
other 12 address combinations is used, an unexpected
combination of pullups might be asserted until the first
I
2
C transmission (to any device, not necessarily the
MAX7323) is put on the bus.
I/O Port Inputs
I/O port inputs switch at the CMOS logic levels as
determined by the expander’s supply voltage, and
are overvoltage tolerant to +6V, independent of the
expander’s supply voltage.
I/O Port Input Transition Detection
All four I/O ports configured as inputs are monitored
for changes since the expander was last accessed
through the serial interface. The state of the I/O ports
is stored in an internal “snapshot” register for transition
monitoring. The snapshot is continuously compared
with the actual input conditions, and if a change is
detected for any port input, INT is asserted to signal a
state change. An internal transition flag is set for that
port. The input ports are sampled (internally latched
into the snapshot register) and the old transition flags
cleared during the I
2
C acknowledge of every MAX7323
read and write access. The previous port transition
flags are read through the serial interface as the second
byte of a 2-byte read sequence.
A long read sequence (more than 2 bytes) can be used
to poll the expander continuously without the overhead
of resending the slave address. If more than 2 bytes are
read from the expander, the expander repeatedly returns
the input port data, alternating with the transition flags.
The inputs are repeatedly resampled and the transition
flags repeatedly reset for each pair of bytes read. All
changes that occur during a long read sequence are
detected and reported.
The INT output is not reasserted during a read sequence
to avoid recursive reentry into an interrupt service routine.
Instead, if a data change occurs that would normally cause
the INT output to be set, the INT assertion is delayed until
the STOP condition. INT is not reasserted upon a STOP
condition if the changed input data is read before the
STOP occurs. The INT logic ensures that unnecessary
interrupts are not asserted, yet data changes are detected
and reported no matter when the change occurs.
Port Outputs
Write 1 byte to the MAX7323 to set the output port levels
for the four push-pull outputs, and the four open-drain
I/O ports simultaneously.
Table 3. MAX7323 Address Map
PIN
CONNECTION
DEVICE ADDRESS OUTPUTS POWER-UP DEFAULT 40kΩ INPUT PULLUPS ENABLED
AD2 AD0 A6 A5 A4 A3 A2 A1 A0 O7 O6 P5 P4 P3 P2 O1 O0 O7 O6 P5 P4 P3 P2 O1 O0
SCL GND 1 1 0 0 0 0 0 1 1 1 1 0 0 0 0
Pullups are not enabled for push-pull outputs.
Y Y — —
Pullups are not enabled for push-pull outputs.
SCL V+ 1 1 0 0 0 0 1 1 1 1 1 1 1 1 1 Y Y Y Y
SCL SCL 1 1 0 0 0 1 0 1 1 1 1 1 1 1 1 Y Y Y Y
SCL SDA 1 1 0 0 0 1 1 1 1 1 1 1 1 1 1 Y Y Y Y
SDA GND 1 1 0 0 1 0 0 1 1 1 1 0 0 0 0 Y Y — —
SDA V+ 1 1 0 0 1 0 1 1 1 1 1 1 1 1 1 Y Y Y Y
SDA SCL 1 1 0 0 1 1 0 1 1 1 1 1 1 1 1 Y Y Y Y
SDA SDA 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 Y Y Y Y
GND GND 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 — — — —
GND V+ 1 1 0 1 0 0 1 0 0 0 0 1 1 1 1 — — Y Y
GND SCL 1 1 0 1 0 1 0 0 0 0 0 1 1 1 1 — — Y Y
GND SDA 1 1 0 1 0 1 1 0 0 0 0 1 1 1 1 — — Y Y
V+ GND 1 1 0 1 1 0 0 1 1 1 1 0 0 0 0 Y Y — —
V+ V+ 1 1 0 1 1 0 1 1 1 1 1 1 1 1 1 Y Y Y Y
V+ SCL 1 1 0 1 1 1 0 1 1 1 1 1 1 1 1 Y Y Y Y
V+ SDA 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 Y Y Y Y
www.maximintegrated.com
Maxim Integrated │ 8
MAX7323 I
2
C Port Expander with 4 Push-Pull
Outputs and 4 Open-Drain I/Os