Slave Address and Input Pullup Selection

Address inputs AD0 and AD2 determine the MAX7323

slave address, select which inputs have pullup resis-

tors, and set the default logic state on outputs. Pullups

are enabled on the input ports in groups of two (see

Table 3). The MAX7319, MAX7321, MAX7322, and

MAX7323 use a different range of slave addresses

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

transmission, regardless of whether the transmission is

actually addressing the MAX7323. The MAX7323 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. Therefore, the

MAX7323 slave address can be configured dynamical-

ly in the application without cycling the device supply.

On initial power-up, the MAX7323 cannot decode

transmission. AD0 and AD2 initially appear to be con-

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

address selection determines the power-up default

states of the output ports and I/O port initial logic state,

and whether pullups are enabled. However, at power-

impedance at the pins of every device (master or slave)

connected to the bus, including the MAX7323. 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 pullup selection logic uses AD0 to

select whether pullups are enabled for ports P2 and P3,

and to set the initial logic state for O0 and O1. AD2

selects whether pullups are enabled for ports P4 and

P5 and sets the initial logic state for O6 and O7. The

rule is that a logic-high, SDA, or SCL connection

selects the pullups and sets the default logic state to

high. A logic-low deselects the pullups and sets the

default logic state low (see Table 3). The port configu-

uration, where SDA or SCL are pulled up to V+ by the

There are circumstances where the assumption that

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

in applications in which there is legitimate bus activity

during power-up. Also, if SDA and SCL are terminated

with pullup resistors to a different supply voltage than

the MAX7323’s supply voltage, and if that pullup supply

rises later than the MAX7323’s supply, then SDA or

SCL may appear at power-up to be connected to GND.

In such applications, use the four address combina-

tions that are selected by connecting address inputs

and 4 Open-Drain I/Os

_______________________________________________________________________________________

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