and 8 Open-Drain I/Os

_______________________________________________________________________________________

7

The open-drain ports offer latching transition detection

when used as inputs. All input ports are continuously

monitored for changes. An input change sets one of 8

flag bits that identify changed input(s). All flags are

cleared upon a subsequent read or write transaction to

the MAX7325.

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 MAX7325 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 2).

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 out-

put state. I/O ports with internal pullups disabled

default to a logic-low output state.

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 groups of four

(see Tables 2 and 3).

Initial Power-Up

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

INT is deasserted. The transition flags are cleared to indi-

cate no data changes. The power-up default states of the

selection inputs, AD0 and AD2 (Tables 2 and 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 MAX7325 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

tents to the POR defaults (Tables 2 and 3).

RST Input

involving the MAX7325, forcing the MAX7325 into the

rupt output (INT).

Standby Mode

When the serial interface is idle, the MAX7325 automatical-

ly enters standby mode, drawing minimal supply current.

Slave Address, Power-Up Default Logic

Levels, and Input Pullup Selection

Address inputs AD0 and AD2 determine the MAX7325

slave address, set the power-up I/O state for the ports,

and select which inputs have pullup resistors. Internal

pullups and power-up default states are set in groups

of four (see Table 2).

transmission, regardless of whether the transmission is

actually addressing the MAX7325. The MAX7325 distin-

guishes whether address inputs AD0 and AD2 are con-

nected to SDA or SCL instead of fixed logic levels V+

or GND during this transmission. The MAX7325 slave

address can be configured dynamically in the applica-

tion without cycling the device supply.

On initial power-up, the MAX7325 cannot decode the

transmission. AD0 and AD2 initially appear to be

PART

SLAVE

ADDRESS

INPUTS

INPUT

INTERRUPT

MASK

OPEN-

DRAIN

OUTPUTS

PUSH-

PULL

OUTPUTS

CONFIGURATION

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.

Table 1. MAX7319–MAX7329 Family Comparison (continued)