case of a hung bus, 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 cleared

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

Use the slave address selection to ensure that I/O ports

used as inputs are high on power-up. To simplify I/O

port and slave address configuration, I/O ports with

internal pullups enabled also default with their open-

drain outputs logic high (high impedance). I/O ports

with internal pullups disabled default with open-drain

outputs logic low. Output port power-up logic levels are

selected by the address select inputs AD0 and AD2.

Ports default to logic high or logic low on power-up in

Initial Power-Up

On power-up, the transition detection logic is reset, and

INT is released to a high-impedance state. The transi-

tion flags are cleared to indicate no data changes. The

power-up default states of the eight I/O ports are set

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.

RST Input

dition. A reset does not affect the interrupt output (INT)

or change the contents of the interrupt mask register.

RST is overvoltage tolerant to +6V.

6

_______________________________________________________________________________________

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

—

PCF8574-, PCF8574A-compatible versions:

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 PORTS IN 24-PIN PACKAGES

MAX7324

8

Yes

—

8

Software equivalent to a MAX7320 plus a MAX7321.

MAX7325

Up to 8

—

Up to 8

8

Software equivalent to a MAX7320 plus a MAX7319.

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. MAX7321–MAX7329 Family Comparison (continued)