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

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

(1.6V max), the POR circuit releases the registers and

2-wire interface for normal operation. When V+ drops to

to the POR defaults (Table 3).

Table 1. MAX7319–MAX7329 Family Comparison (continued)

PART

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