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MAX7319

I2C Port Expander with Eight Inputs and Maskable Transition Detection

Maxim Integrated 

MAX7319

I2C Port Expander with Eight Inputs

and Maskable Transition Detection

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

PART

I2C SLAVE

ADDRESS

INPUTS

MAX7319 110xxxx

8

MAX7320 101xxxx

—

MAX7321 110xxxx Up to 8

MAX7322 110xxxx

4

MAX7323 110xxxx Up to 4

MAX7328 0100xxx Up to 8

MAX7329 0111xxx Up to 8

INTERRUPT

MASK

Yes

—

—

Yes

—

—

—

OPEN-

RAIN

OUTPUTS

—

—

Up to 8

—

Up to 4

Up to 8

Up to 8

PUSH-

PULL I2C DATA WRITE

OUTPUTS

I2C DATA READ

—

<I7–I0 interrupt

mask>

<I7–I0 port inputs>

<I7–I0 transition flags>

8

<O7–O0 port

outputs>

<O7–O0 port inputs>

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

<P7–P0 transition flags>

<O7, O6 outputs, <O7, O6, I5–I2, O1, O0

4

I5–I2 interrupt

mask, O1, O0

Port inputs>

<0, 0, I5–I2 transition flags,

outputs>

0, 0>

<O7, O6, P5–P2, O1, O0

4

<port outputs>

Port inputs>

<0, 0, P5–P2 transition flags,

0, 0>

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

—

<P7–P0 port

outputs>

<P7–P0 port inputs>

of the I2C specification. Therefore, address inputs AD2

and AD0 that are connected to SDA or SCL normally

appear at power-up to be connected to V+. The pullup

selection logic uses AD0 to select whether pullups are

enabled for ports I3–I0, and uses AD2 to select whether

pullups are enabled for ports I7–I4. The rule is that a

logic-high SDA or SCL connection selects the pullups,

while a logic-low deselects the pullups (Table 3). The

pullup configuration is correct on power-up for a standard

I2C configuration, where SDA and SCL are pulled up to

V+ by the external I2C pullup 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

legitimate bus activity during power-up. Also, if SDA and

SCL are terminated with pullup resistors to a different

supply voltage than the MAX7319’s supply voltage, and

if that pullup supply rises later than the MAX7319’s

supply, then SDA or SCL may appear at power-up to be

connected to GND. In such applications, use the four

address combinations that are selected by connecting

address inputs AD2 and AD0 to V+ or GND (shown in

bold in Table 3). These selections are guaranteed to be

correct at power-up, independent of SDA and SCL

behavior. If one of the other 12 address combinations is

used, be aware that an unexpected combination of

pullups might be asserted until the first I2C

transmission (to any device, not necessarily the MAX7319)

is put on the bus.

Port Inputs

Port inputs switch at CMOS logic levels as determined by

the expander’s supply voltage, and are overvoltage toler-

ant to +6V, independent of the expander’s supply voltage.

Port-Input Transition Detection

All eight input ports are monitored for changes since

the expander was last accessed through the serial

interface. The state of the input ports is stored in an

internal “snapshot” register for transition monitoring.

The snapshot is continuously compared with the actual

input conditions, and if a change is detected for any

port input, an internal transition flag is set for that port.

The eight port inputs are sampled (internally latched

into the snapshot register) and the old transition flags

cleared during the I2C acknowledge of every MAX7319

read and write access. The previous port transition

flags are read through the serial interface as the sec-

ond byte of a 2-byte read sequence.

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