MAX7322
I2C Port Expander with
4 Push-Pull Outputs and 4 Inputs
_______________________________________________________________________________________
7
When the MAX7322 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 MAX7322.
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 output
INT and all transition flags are deasserted when the
MAX7322 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).
Output port power-up logic states 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 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 state of
the four push-pull outputs are set according to the I2C
slave address selection inputs, AD0 and AD2 (Table 2).
Power-On Reset (POR)
The MAX7322 contains an integral POR circuit that
ensures all registers are reset to a known state on
power-up. When V+ rises above VPOR (1.6V max), the
POR circuit releases the registers and 2-wire interface
for normal operation. When V+ drops to less than VPOR,
the MAX7322 resets all register contents to the POR
defaults (Table 2).
RST Input
The active-low RST input operates as a reset that voids
any current I2C transaction involving the MAX7322,
forcing the MAX7322 into the I2C STOP condition. The
reset action does not clear the interrupt output (INT).
Standby Mode
When the serial interface is idle, the MAX7322 automat-
ically enters standby mode, drawing minimal supply
current.
Slave Address and Input Pullup
Selection/Default Logic State
Address inputs AD0 and AD2 determine the MAX7322
slave address, select which inputs have pullup resis-
tors and set the default logic state for outputs. Pullups
are enabled on the input ports in groups of two (see
Table 2). The MAX7319, MAX7321, MAX7322, and
MAX7323 use a different range of slave addresses
(110xxxx) than the MAX7320 (101xxxx).
The MAX7322 slave address is determined on each I2C
transmission, regardless of whether the transmission is
actually addressing the MAX7322. The MAX7322 distin-
guishes whether address inputs AD2 and AD0 are con-
nected to SDA or SCL instead of fixed logic levels V+ or
GND during this transmission. This means that the
MAX7322 slave address can be configured dynamically
in the application without cycling the device supply.
PART
I2C
SLAVE
ADDRESS
INPUTS
INPUT
INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
I2C DATA
WRITE
I2C DATA
READ
APPLICATION
16-PORT EXPANDERS
MAX7324
8
Yes
—
8
—
Software equivalent to a
MAX7320 plus a MAX7319.
MAX7325
Up to 8
—
Up to 8
8
—
Software equivalent to a
MAX7320 plus a MAX7321.
MAX7326
4
Yes
—
12
—
Software equivalent to a
MAX7320 plus a MAX7322.
MAX7327
101xxxx
and
110xxxx
Up to 4
—
Up to 4
12
—
Software equivalent to a
MAX7320 plus a MAX7323.
Table 1. MAX7319–MAX7329 Family Comparison (continued)