Datasheet

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 2-byte read).
A single-byte write to the MAX7319 sets the interrupt
mask register, and clears both the internal transition
flags and the INT output.
A multibyte write to the MAX7319 sets the interrupt
mask register repeatedly.
Reading from the MAX7319
A read from the MAX7319 starts with the master
transmitting the MAX7319’s slave address with the R/W
bit set high. The MAX7319 acknowledges the slave
address and samples the input ports during acknowledge
bit. INT deasserts during the slave address acknowledge.
Typically, the master reads 1 or 2 bytes from the MAX7319,
with each byte, except the last one, being acknowledged
by the master upon reception.
When the master reads 1 byte from the MAX7319 and
subsequently issues a STOP condition (Figure 6), the
MAX7319 transmits the current port data, clears the
transition flags, and resets the transition detection. INT
deasserts during the slave address acknowledge. The
new snapshot data is the current port data transmitted
to the master; therefore, port transitions ocurring during
the transmission are detected. INT remains high until the
STOP condition.
When the master reads 2 bytes from the MAX7319 and
subsequently issues a STOP condition (Figure 7), the
MAX7319 transmits the current port data, followed by
the transition flags. The transition flags are cleared, and
transition detection reset. INT deasserts during the
slave address acknowledge. The new snapshot data is
the current port data transmitted to the master; there-
fore, port transitions occurring during the transmission
are detected. INT remains high until the STOP condi-
tion. When the master reads more than 2 bytes, the input
port data alternates with the transition flag.
Figure 7. Reading from the MAX7319 (2 Data Bytes)
SCL
MAX7319 SLAVE ADDRESS A011S P1
PORTS
INT OUTPUT
R/W
PORT SNAPSHOT
t
IV
t
PH
t
IR
A
I0
I1
I2I3I4I5
I6
I7
D0D1D2D3D4D5D6D7
PORT SNAPSHOT PORT SNAPSHOT
t
PSU
t
IP
F0
F1
F2F3F4F5
F6
F7
D7 D6 D5 D4 D3 D2 D1 D0 N
INT REMAINS HIGH UNTIL STOP CONDITION
PORT INPUTS INTERRUPT FLAGS
S = START CONDITION SHADED = SLAVE TRANSMISSION
P = STOP CONDITION N = NOT ACKNOWLEDGE
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Maxim Integrated │ 11
MAX7319 I
2
C Port Expander with Eight Inputs
and Maskable Transition Detection