Datasheet

case of a bus lockup, terminating any serial transaction to
or from the MAX7321.
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.
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.
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.
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).
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. 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).
Initial Power-Up
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
of the eight I/O ports are set according to the I
2
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.
Power-On Reset
The MAX7321 contains an integral power-on reset
(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 MAX7321 resets all register contents
to the POR defaults (Table 3).
Table 1. MAX7319–MAX7329 Family Comparison (continued)
PART
I
2
C
SLAVE
ADDRESS
INPUTS
INPUT
INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
APPLICATION
MAX7323 110xxxx Up to 4 — Up to 4 4
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.
MAX7328
MAX7329
0100xxx
0111xxx
Up to 8 — Up to 8 —
8 open-drain I/O ports with nonlatching transition
detection interrupt and pullups on all ports.
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
101xxxx
And
110xxxx
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 Up to 4 — Up to 4 12 Software equivalent to a MAX7320 plus a MAX7323.
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MAX7321 I
2
C Port Expander with 8 Open-Drain I/Os