2
MAX7321
I C Port Expander with 8 Open-Drain I/Os
Table 1. MAX7319–MAX7329 Family Comparison (continued)
2
I C
INPUT
INPUTS INTERRUPT
MASK
OPEN-
DRAIN
PUSH-
PULL
PART
SLAVE
APPLICATION
ADDRESS
OUTPUTS OUTPUTS
4 I/O, 4 output-only versions:
4 open-drain I/O ports with latching transition
detection interrupt and selectable pullups.
4 push-pull outputs with selectable power-up default
levels.
MAX7323
110xxxx
Up to 4
—
—
Up to 4
4
8 open-drain I/O ports with nonlatching transition
detection interrupt and pullups on all ports.
MAX7328
MAX7329
0100xxx
0111xxx
Up to 8
Up to 8
—
All ports power up as inputs (or logic-high outputs).
Any port can be used as an input by setting the open-
drain output to logic-high.
16-PORT EXPANDERS
MAX7324
8
Yes
—
—
8
8
Software equivalent to a MAX7320 plus a MAX7319.
Software equivalent to a MAX7320 plus a MAX7321.
Software equivalent to a MAX7320 plus a MAX7322.
Software equivalent to a MAX7320 plus a MAX7323.
101xxxx
MAX7325
Up to 8
4
Up to 8
—
And
MAX7326
Yes
—
12
12
110xxxx
MAX7327
Up to 4
Up to 4
case of a bus lockup, terminating any serial transaction to
or from the MAX7321.
internal pullups enabled default to a logic-high output
state. Ports with internal pullups disabled default to a
logic-low output state. 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 four (see Table 3).
Any port can be configured as a logic input by setting the
port output logic-high (logic-high for an open-drain output
is high impedance). When the MAX7321 is read through
the serial interface, the actual logic levels at the ports are
read back.
Initial Power-Up
The open-drain ports offer latching transition detection
when used as inputs. All input ports are continuously
monitored for changes. An input change sets 1 of 8 flag
bits that identify changed input(s). All flags are cleared
upon a subsequent read or write transaction to the
MAX7321.
On power-up, the transition detection logic is reset, and
INT is deasserted. The transition flags are cleared to
indicate no data changes. The power-up default states
2
of the eight I/O ports are set according to the I C slave
address selection inputs, AD0 and AD2 (Table 3). For
I/O ports used as inputs, ensure that the default
states are logic-high so that the I/O ports power up
in the high-impedance state. All I/O ports configured
with pullups enabled also have a logic-high power-up
state.
A latching interrupt output (INT) is programmed to flag
logic changes on ports used as inputs. Data changes
on any input port forces INT to a logic-low. Changing
the I/O port level through the serial interface does not
cause an interrupt. The interrupt output INT is deassert-
ed when the MAX7321 is next accessed through the
serial interface.
Power-On Reset
The MAX7321 contains an integral power-on reset
(POR) circuit that ensures all registers are reset to a
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 four (see Table 3).
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
Use the slave address selection to ensure that I/O ports
used as inputs are logic-high on power-up. I/O ports with
less than V
to the POR defaults (Table 3).
, the MAX7321 resets all register contents
POR
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