Datasheet

Writing to the MAX7319
A write to the MAX7319 starts with the master transmit-
ting the MAX7319’s slave address with the R/W bit set
low. The MAX7319 acknowledges the slave address,
and samples the input ports during the acknowledge
bit. INT deasserts during the slave address
acknowledge. The master can now transmit 1 or more
bytes of data. The MAX7319 acknowledges these
subsequent bytes of data and updates the interrupt mask
register with each new byte until the master issues a
STOP condition (Figure 8).
Applications Information
Port Input and I
2
C Interface Level Translation
from Higher or Lower Logic Voltages
The MAX7319 I2C interface (SDA, SCL, AD0, AD2), reset
input RST, interrupt output INT, and the eight input ports
I0–I7 are overvoltage protected to +6V independent of
V+. This allows the MAX7319 to operate from a lower
supply voltage, such as +3.3V, while the I
2
C interface
and/or any of the eight input ports are driven from a higher
logic level, such as +5V.
The MAX7319 can operate from a higher supply
voltage, such as +3V, while the I
2
C interface and/or
some of the input ports I0–I7 are driven from a lower
logic level, such as +2.5V. Apply a minimum voltage
of 0.7 x V+ to assert a logic-high on any input. For
example, a MAX7319 operating from a +5V supply may
not recognize a +3.3V nominal logic-high. One solution
for input level translation is to drive the MAX7319 inputs
from open-drain outputs. Use a pullup resistor to V+ or a
higher supply to ensure a high logic voltage of greater
than 0.7 x V+.
Hot Insertion
RST, SCL, SDA, AD0, and AD2 remain high impedance
with up to +6V asserted on them when the MAX7319 is
powered down (V+ = 0). The MAX7319 can therefore be
used in hot-swap applications.
Each of the input ports I0–I7 has a protection diode
to GND (Figure 9). When a port input is driven to a
voltage lower than GND, the protection diode clamps the
voltage to a diode drop below GND.
Each of the input ports I0–I7 also has a 40kΩ (typ)
pullup resistor that can be enabled or disabled. When
a port input is driven to a voltage higher than V+, the
body diode of the pullup enable switch conducts and
the 40kΩ pullup resistor is enabled. When the
MAX7319 is powered down (V+ = 0), every input port
appears as a 40kΩ resistor in series with a diode
connected to GND. Input ports are protected to +6V under
any of these circumstances (Figure 9).
Figure 9. Input Port Structure
Figure 8. Writing to the MAX7319
P
I0–I7
PULLUP
ENABLE
INPUT
40kΩ
MAX7319
V+
V+
SCL
SDA
START CONDITION R/W
SLAVE ADDRESS
S 0
1 2 3 4 5 6 7 8
A A A
t
PV
DATA 1 DATA 2
t
PV
DATA TO INTERRUPT MASK DATA TO INTERRUPT MASK
S = START CONDITION SHADED = SLAVE TRANSMISSION
P = STOP CONDITION N = NOT ACKNOWLEDGE
www.maximintegrated.com
Maxim Integrated │ 12
MAX7319 I
2
C Port Expander with Eight Inputs
and Maskable Transition Detection