MAX7326
I
2
C Port Expander with 12 Push-Pull Outputs
and 4 Inputs
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When the MAX7326 is read through the serial interface,
the actual logic levels at the ports are read back.
The four input ports offer latching transition detection
functionality. 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 MAX7326.
A latching interrupt output, INT, is programmed to flag
input data changes on the four input ports through an
interrupt mask register. By default, data changes on
any input port force INT to a logic-low. The interrupt out-
put INT and all transition flags are deasserted when the
MAX7326 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).
Initial Power-Up
On power-up, the transition detection logic is reset, and
INT is deasserted. The interrupt mask register is set to
0x3C, enabling the interrupt output for transitions on all
four input ports. The transition flags are cleared to indi-
cate no data changes. The power-up default states of
the 12 push-pull outputs are set according to the I
2
C
slave address selection inputs, AD0 and AD2 (see
Tables 2 and 3). Pullups are enabled on the input port
in groups of two (see Table 2).
Power-On Reset (POR)
The MAX7326 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 below V
POR
, the
MAX7326 resets all output register contents to the POR
defaults (Tables 2 and 3).
RST
Input
The active-low RST input operates as a reset that voids
any I
2
C transaction involving the MAX7326 and forcing
the MAX7326 into the I
2
C STOP condition. The reset
action does not clear the interrupt output (INT).
Standby Mode
When the serial interface is idle, the MAX7326 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 MAX7326
slave address and select which inputs have pullup
resistors. Pullups are enabled on the input ports in
groups of two (see Table 2).
The MAX7326 slave address is determined on each I
2
C
transmission, regardless of whether the transmission is
actually addressing the MAX7326. The MAX7326 distin-
guishes whether address inputs AD0 and AD2 are con-
nected to SDA or SCL instead of fixed logic levels V+
or GND during this transmission. This means that the
MAX7326 slave address can be configured dynamically
in the application without cycling the device supply.
On initial power-up, the MAX7326 cannot decode
address inputs AD0 and AD2 fully until the first I
2
C
transmission. This is important because the address
selection is used to determine the power-up logic state
(output low or I/O high), and whether pullups are
enabled. However, at power-up, the I
2
C SDA and SCL
bus interface lines are high impedance at the pins of
every device (master or slave) connected to the bus,
including the MAX7326. This is guaranteed as part of
the I
2
C specification. Therefore, when address inputs
AD0 and AD2 are connected to SDA or SCL during
power-up, they appear to be connected to V+. The port
