Datasheet

data is the current port data transmitted to the master,
so any input port changes occurring during the
transmission are detected. INT remains high until the
STOP condition.
Writing to the MAX7322
A write to the MAX7322 starts with the master trans-
mitting the MAX7322’s slave address with the R/W
bit set low. The MAX7322 acknowledges the slave
address, and samples the ports (takes a snapshot) during
acknowledge. INT deasserts during the slave
acknowledge. The master proceeds to transmit 1 or
more bytes of data. The MAX7322 acknowledges these
subsequent bytes of data and updates the four output
ports and the 4-bit 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 MAX7322’s SDA, SCL, AD0, AD2, input RST, INT,
and input ports I2–I5 are overvoltage protected to +6V
independent of V+. This allows the MAX7322 to operate
from a lower supply voltage, such as +3.3V, while the I
2
C
interface and/or some of the four input ports are driven
from a higher logic level, such as +5V.
The MAX7322 can operate from a higher supply voltage,
such as +3V, while the I
2
C interface and/or some of the
four input ports I2–I5 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 MAX7322
operating from a +5V supply may not recognize a +3.3V
nominal logic-high. One solution for input-level translation
is to drive the MAX7322 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+.
Figure 8. Writing to the MAX7322
SCL
SDA
START CONDITION R/W ACKNOWLEDGE
FROM SLAVE
SLAVE ADDRESS
S 0
1 2 3 4 5 6 7 8
A A A
t
PV
DATA 1 DATA 2
DATA 2 VALIDDATA 1 VALID
INTERNAL WRITE
TO PORT
DATA OUT
FROM PORT
ACKNOWLEDGE
FROM SLAVE
ACKNOWLEDGE
FROM SLAVE
t
PV
DATA TO INTERRUPT MASK DATA TO INTERRUPT MASK
S = START CONDITION
P = STOP CONDITION
SHADED = SLAVE TRANSMISSION
N = NOT ACKNOWLEDGE
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Maxim Integrated │ 13
MAX7322 I
2
C Port Expander with
4 Push-Pull Outputs and 4 Inputs