MAX7321 Maxim, MAX7321 Datasheet - Page 10

• Manufacturer Part Number: MAX7321
• Description: The MAX7321 2-wire serial-interfaced peripheral features eight open-drain I/O ports with selectable internal pullups and transition detection
• Manufacturer: Maxim

The MAX7321 is accessed through an I
transition flags are cleared, and INT is deasserted each
time the device acknowledges the I
A single-byte read from the MAX7321 returns the sta-
tus of the eight I/O ports.
A 2-byte read returns first the status of the eight I/O
ports (as for a single-byte read), followed by the transi-
tion flags.
A multibyte read (more than 2 bytes before the I
STOP bit) repeatedly returns the port data, alternating
with the transition flags. As the port data is resampled
for each transmission, and the transition flags are reset
each time, a multibyte read continuously returns the
current data and identifies any changing ports.
If a port data change occurs during the read sequence,
INT is reasserted after the I
does not generate another interrupt during a single-
byte or multibyte read.
Port data is sampled during the preceding I
acknowledge bit (the acknowledge bit for the I
address in the case of a single-byte or 2-byte read).
A single-byte write to the MAX7321 sets the logic state
of all eight I/O ports.
A multibyte write to the MAX7321 repeatedly sets the
logic state of all eight I/O ports.
A read from the MAX7321 starts with the master trans-
mitting the MAX7321’s slave address with the R/W bit
set high. The MAX7321 acknowledges the slave
address, and samples the ports during the acknowl-
edge bit. INT deasserts during the slave address
acknowledge.
Typically, the master reads 1 or 2 bytes from the
MAX7321, each byte being acknowledged by the mas-
ter upon reception with the exception of the last byte.
When the master reads 1 byte from the MAX7321 and
subsequently issues a STOP condition (Figure 6), the
MAX7321 transmits the current port data, clears the
change flags, and resets the transition detection. INT
deasserts during the slave acknowledge. The new
snapshot data is the current port data transmitted to the
master; therefore, port changes ocurring during the
I
10
2
C Port Expander with 8 Open-Drain I/Os
______________________________________________________________________________________
Reading from the MAX7321
2
C STOP bit. The MAX7321
Accessing the MAX7321
2
C slave address.
2
C interface. The
2
C slave
2
2
C
C
transmission are detected. INT remains high until the
STOP condition.
The master can read 2 bytes from the MAX7321 and
then issue a STOP condition
MAX7321 transmits the current port data, followed by the
change flags. The change flags are then cleared, and
transition detection resets. INT goes high (high imped-
ance if an external pullup resistor is not fitted) during the
slave acknowledge. The new snapshot data is the cur-
rent port data transmitted to the master; therefore, port
changes occurring during the transmission are detected.
INT remains high until the STOP condition.
Figure 3. Bit Transfer
Figure 4. Acknowledge
TRANSMITTER
SDA
SCL
RECEIVER
SDA BY
SDA BY
SCL
CONDITION
START
DATA LINE STABLE;
S
DATA VALID
1
CHANGE OF DATA
ALLOWED
2
(Figure 7). In this case, the
FOR ACKNOWLEDGMENT
CLOCK PULSE
8
9