Standby Mode

When the serial interface is idle, the MAX7321 automat-

ically 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 MAX7321

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

and MAX7323 use a different range of slave addresses

(110xxxx) than the MAX7320 (101xxxx) (Table 2).

transmission, regardless of whether the transmission is

actually addressing the MAX7321. The MAX7321 distin-

guishes whether address inputs AD2 and AD0 are con-

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

GND during this transmission. This means that the

MAX7321 slave address can be configured dynamical-

ly in the application without cycling the device supply.

On initial power-up, the MAX7321 cannot decode

transmission, and AD0 and AD2 initially appear to be

connected to V+ or GND. This is important because the

address selection is used to determine the power-up

logic level (output low or input/output high), and

whether pullups are applied. However, at power-up, the

ance at the pins of every device (master or slave) con-

nected to the bus, including the MAX7321. This is

address inputs AD2 and AD0 that are connected to

SDA or SCL normally appear at power-up to be con-

nected to V+. The power-up logic uses AD0 to select

the power-up state and whether pullups are enabled for

ports P3–P0, and AD2 for ports P7–P4. The rule is that

a logic high, SDA, or SCL connection selects the

pullups (and sets the default port condition to input or

logic-high output), while a logic low deselects the

pullups (and sets the default port condition to logic-low

resistors.

There are circumstances where the assumption that

SDA = SCL = V+ on power-up is not true—for example,

in true hot-swap applications in which there is legiti-

_______________________________________________________________________________________

7

PART

ADDRESS

INPUTS

INTERRUPT

MASK

OPEN-

DRAIN

OUTPUTS

PUSH-

PULL

OUTPUTS

MAX7319

110xxxx

8

Yes

—

—

<I7–I0 interrupt

mask>

<I7–I0 port inputs>

<I7–I0 transition flags>

MAX7320

101xxxx

——

—

8

<O7–O0 port

outputs>

<O7-O0 port inputs>

MAX7321

110xxxx

Up to 8

—

Up to 8

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

<P7–P0 transition flags>

MAX7322

110xxxx

4

Yes

—

4

<O7, O6 outputs,

I5–I2 interrupt

mask, O1, O0

outputs>

<O7, O6, I5–I2, O1, O0 port

inputs>

<0, 0, I5–I2 transition flags,

0, 0>

MAX7323

110xxxx

Up to 4

—

Up to 4

4

<port outputs>

<O7, O6, P5–P2, O1, O0 port

inputs>

<0, 0, P5–P2 transition flags,

0, 0>

MAX7328

0100xxx

Up to 8

—

Up to 8

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

MAX7329

0111xxx

Up to 8

—

Up to 8

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

Table 2. Read and Write Access to Eight-Port Expander Family