MAX7322 Datasheet, PDF (10/18 Pages) Maxim Integrated Products – I2C Port Expander with 4 Push-Pull Outputs and 4 Inputs

I²C Port Expander with
4 Push-Pull Outputs and 4 Inputs
SDA operates as both an input and an open-drain out-
put. A pullup resistor, typically 4.7kΩ, is required on
SDA. SCL operates only as an input. A pullup resistor,
typically 4.7kΩ, is required on SCL if there are multiple
masters on the 2-wire interface, or if the master in a sin-
gle-master system has an open-drain SCL output.
Each transmission consists of a START condition sent
by a master, followed by the MAX7322’s 7-bit slave
address plus R/W bit, one or more data bytes, and
finally a STOP condition (Figure 2).
START and STOP Conditions
Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis-
sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master
has finished communicating with the slave, the master
issues a STOP (P) condition by transitioning SDA from
low to high while SCL is high. The bus is then free for
another transmission (Figure 2).
Bit Transfer
One data bit is transferred during each clock pulse.
The data on SDA must remain stable while SCL is high
(Figure 3).
Acknowledge
The acknowledge bit is a clocked 9th bit the recipient
uses to acknowledge receipt of each byte of data
(Figure 4). Each byte transferred effectively requires 9
bits. The master generates the 9th clock pulse, and the
recipient pulls down SDA during the acknowledge
clock pulse, such that the SDA line is stable low during
the high period of the clock pulse. When the master is
transmitting to the MAX7322, the MAX7322 generates
the acknowledge bit because the device is the recipi-
ent. When the MAX7322 is transmitting to the master,
the master generates the acknowledge bit because the
master is the recipient.
SDA
SCL
DATA LINE STABLE; CHANGE OF DATA
DATA VALID
ALLOWED
Figure 3. Bit Transfer
SDA
SCL _S
START
CONDITION
Figure 2. START and STOP Conditions
P
STOP
CONDITION
START
CONDITION
SCL
1
SDA BY
TRANSMITTER
SDA BY
RECEIVER S
Figure 4. Acknowledge
CLOCK PULSE
FOR ACKNOWLEDGMENT
2
8
9
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