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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 3. MAX7319 Address Map

PIN CONNECTION

DEVICE ADDRESS

40kΩ INPUT PULLUP ENABLED

AD2

AD0

A6 A5 A4 A3 A2 A1 A0 I7 I6 I5 I4 I3 I2 I1 I0

SCL

GND

1

1

0

0

0

0

0

Y Y Y Y ————

SCL

V+

1

1

0

0

0

0

1

YYYYYYYY

SCL

SCL

1

1

0

0

0

1

0

YYYYYYYY

SCL

SDA

1

1

0

0

0

1

1

YYYYYYYY

SDA

GND

1

1

0

0

1

0

0

Y Y Y Y ————

SDA

V+

1

1

0

0

1

0

1

YYYYYYYY

SDA

SCL

1

1

0

0

1

1

0

YYYYYYYY

SDA

SDA

1

1

0

0

1

1

1

YYYYYYYY

GND

GND

1

1

0

1

0

0

0 ————————

GND

V+

1

1

0

1

0

0

1 ———— Y Y Y Y

GND

SCL

1

1

0

1

0

1

0 ———— Y Y Y Y

GND

SDA

1

1

0

1

0

1

1 ———— Y Y Y Y

V+

GND

1

1

0

1

1

0

0

Y Y Y Y ————

V+

V+

1

1

0

1

1

0

1

YYYYYYYY

V+

SCL

1

1

0

1

1

1

0

YYYYYYYY

V+

SDA

1

1

0

1

1

1

1

YYYYYYYY

A long read sequence (more than 2 bytes) can be used

to poll the expander continuously without the overhead

of resending the slave address. If more than 2 bytes are

read from the expander, the expander repeatedly returns

the input port data followed by the transition flags. The

inputs are repeatedly resampled and the transition flags

repeatedly reset for each pair of bytes read. All changes

that occur during a long read sequence are detected and

reported.

The MAX7319 includes an 8-bit interrupt mask register

that selects which inputs generate an interrupt upon

change. Each input’s transition flag is set when its input

changes, independent of the interrupt mask register

settings. The interrupt mask register allows the processor

to be interrupted for critical events, while the inputs and

the transition flags can be polled periodically to detect

less critical events.

The INT logic ensures that unnecessary interrupts are

not asserted, yet data transitions are detected and

reported regardless of when the transition occurs. The

INT output is not reasserted during a read sequence to

avoid recursive reentry into an interrupt service routine. If

transition occurs during read sequence, the INT assertion

is delayed until the STOP condition, however, INT is not

reasserted upon a STOP condition if the changed input

data is read before the STOP occurs.

Transition-Detection Masks

The transition-detection logic incorporates a transition

flag and an interrupt mask bit for each input port. The

eight change flags can be read through the serial

interface, and the 8-bit interrupt mask is set through the

serial interface.

Each port’s transition flag is set when that port’s input

changes, and the transition flag remains set even if the

input returns to its original state. The port’s interrupt

mask determines whether a transition on that input port

generates an interrupt. Enable interrupts for high-priority

inputs using the interrupt mask. The interrupt allows the

system to respond quickly to changes on these inputs.

Poll the MAX7319 periodically to monitor less-important

inputs. The transition flags indicate whether a permanent

or transient change has occurred on any input since the

MAX7319 was last accessed.

Serial Interface

Serial Addressing

The MAX7319 operates as a slave that sends and

receives data through an I2C interface. The interface uses

a serial data line (SDA) and a serial clock line (SCL) to

achieve bidirectional communication between master(s)

and slave(s). The master initiates all data transfers to

and from the MAX7319 and generates the SCL clock that

synchronizes the data transfer (Figure 1).

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