MAX7327
I
2
C Port Expander with 12 Push-Pull
Outputs and 4 Open-Drain I/Os
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The four open-drain ports offer latching transition
detection functionality when used as inputs. All input
ports are continuously monitored for changes. An input
change sets 1 of 4 flag bits that identify the changed
input(s). All flags are cleared upon a subsequent read
or write transaction to the MAX7327.
A latching interrupt output INT automatically flags data
changes on any of the I/O ports used as inputs through
an interrupt mask register. Data changes on any input
port forces INT to a logic-low. The interrupt output INT
is deasserted when the MAX7327 is next accessed
through the serial interface.
Internal pullup resistors to V+ are selected by the
address select inputs, AD0 and AD2. Pullups are enabled
on the input ports in groups of two (see Table 2). Use the
slave address selection to ensure that I/O ports used
as inputs are logic-high on power-up. I/O ports with
internal pullups enabled default to a logic-high output
state. I/O ports with internal pullups disabled default to
a logic-low output state.
Output port power-up logic levels are selected by the
address select inputs AD0 and AD2. Ports default to
logic-high or logic-low on power-up in groups of two
(see Tables 2 and 3).
Initial Power-Up
On power-up, the default states of the 12 push-pull out-
put ports and the four open-drain I/O ports are set
according to the I
2
C slave address selection inputs,
AD0 and AD2 (see Tables 2 and 3). For I/O ports used
as inputs, ensure that the default states are logic-high;
therefore, the I/O ports power up in the high-imped-
ance state. All I/O ports configured with pullups
enabled also have a logic-high default state. On power-
up, the transition detection logic is reset, and INT is
deasserted. The transition flags are cleared, indicating
no data changes.
Power-On Reset (POR)
The MAX7327 contains an integral POR circuit that
ensures all registers are reset to a known state on
power-up. When V+ rises above V
POR
(1.6V max), the
POR circuit releases the registers and 2-wire interface
for normal operation. When V+ drops to less than V
POR
,
the MAX7327 resets all register contents to the POR
defaults (Tables 2 and 3).
RST
Input
The active-low RST input operates as a hardware reset
that voids any I
2
C transaction involving the MAX7327,
forcing the MAX7327 into the I
2
C STOP condition. A
reset does not affect the interrupt output (INT).
Standby Mode
When the serial interface is idle, the MAX7327 automat-
ically enters standby mode drawing minimal supply
current.
Slave Address, Power-Up Default Logic
Levels, and Input Pullup Selection
Address inputs AD0 and AD2 determine the MAX7327
slave address and select which inputs have pullup
resistors. Pullups are enabled on the input ports in
groups of two (see Table 2).
The MAX7327 slave address is determined on each I
2
C
transmission, regardless of whether the transmission is
actually addressing the MAX7327. The MAX7327 distin-
guishes whether address inputs AD0 and AD2 are con-
nected to SDA or SCL instead of fixed-logic levels V+
or GND during the transmission. The MAX7327 slave
detection interrupt and selectable pullups.
levels.
detection interrupt and pullups on all ports.
