Datasheet

MAX7325
I
2
C Port Expander with 8 Push-Pull
and 8 Open-Drain I/Os
12
Maxim Integrated
If a port input data change occurs during the read
sequence, then INT is reasserted during the I
2
C STOP
bit. The MAX7325 does not generate another interrupt
during a single-byte or multibyte read.
Input port data is sampled during the preceding I
2
C
acknowledge bit (the acknowledge bit for the I
2
C slave
address in the case of a single-byte or two-byte read).
A multibyte read from the push-pull ports of the
MAX7325 repeatedly returns the status of the eight out-
put ports, read back as inputs.
A single-byte write to either port groups of the
MAX7325 sets the logic state of all eight ports.
A multibyte write to either port group of the MAX7325
repeatedly sets the logic state of all eight ports.
Reading the MAX7325
A read from the open-drain I/O ports of the MAX7325
starts with the master transmitting the port group’s
slave address with the R/W bit set to high. The
MAX7325 acknowledges the slave address, and sam-
ples the ports during the acknowledge bit. INT
deasserts during the slave address acknowledge.
Typically, the master reads 1 or 2 bytes from the
MAX7325, each byte being acknowledged by the mas-
ter upon reception with the exception of the last byte.
When the master reads one byte from the open-drain
ports of the MAX7325 and subsequently issues a STOP
condition (Figure 6), the MAX7325 transmits the current
port data, clears the change flags, and resets the tran-
sition detection. INT deasserts during the slave
SCL
MAX7325 SLAVE ADDRESS
S1 1 0 A
P
1
PORT
t
IV
N
P0
ACKNOWLEDGE
FROM MASTER
ACKNOWLEDGE
FROM MAX7325
P1
P2P3P4P5
P6
P7
D0D1D2D3D4D5D6D7
PORT I/O
INT OUTPUT
R/W
PORT SNAPSHOT
t
PH
t
IR
PORT SNAPSHOT
S = START CONDITION SHADED = SLAVE TRANSMISSION
P = STOP CONDITION N = NOT ACKNOWLEDGE
t
PSU
t
IP
INT REMAINS HIGH UNTIL STOP CONDITION
Figure 6. Reading Open-Drain Ports of the MAX7325 (1 Data Byte)