Datasheet

RST Input
The RST input voids any I
2
C transaction involving the
MAX7321, forcing the MAX7321 into the I
2
C STOP
condition. A reset does not affect the INT interrupt output.
Standby Mode
When the serial interface is idle, the MAX7321 automat-
ically enters standby mode, drawing minimal supply
current.
Slave Address, Power-Up Default Logic
Levels, and Input Pullup Selection
Address inputs AD0 and AD2 determine the MAX7321
slave address, set the power-up I/O state for the ports,
and select which inputs have pullup resistors. Internal
pullups and power-up default states are set in groups
of four (Table 3). The MAX7319, MAX7321, MAX7322,
and MAX7323 use a different range of slave addresses
(110xxxx) than the MAX7320 (101xxxx) (Table 2).
The MAX7321 slave address is determined on each I
2
C
transmission, regardless of whether the transmission
is actually addressing the MAX7321. The MAX7321
distinguishes whether address inputs AD2 and AD0 are
connected to SDA or SCL instead of fixed logic levels
V+ or GND during this transmission. This means that the
MAX7321 slave address can be configured dynamically in
the application without cycling the device supply.
On initial power-up, the MAX7321 cannot decode
address inputs AD0 and AD2 fully until the first I
2
C
transmission. AD0 and AD2 initially appear to be
connected to V+ or GND. This is important because the
address selection is used to determine the power-up
logic state and whether pullups are enabled. However,
at power-up, the I
2
C SDA and SCL bus interface lines
are high impedance at the pins of every device (master
or slave) connected to the bus, including the MAX7321.
This is guaranteed as part of the I
2
C specification.
Therefore, address inputs AD2 and AD0 that are
connected to SDA or SCL normally appear at power-up to
be connected to V+. The power-up logic uses AD0 to
select the power-up state and whether pullups are
enabled for ports P3–P0, and AD2 for ports P7–P4.
The rule is that a logic-high, SDA, or SCL connection
selects the pullups and sets the default logic state to
high. A logic-low deselects the pullups and sets the
default logic state to low (Table 3). The port configu-
ration is correct on power-up for a standard I
2
C configu
ration, where SDA or SCL are pulled up to V+ by the
external I
2
C pullup resistors.
Table 2. Read and Write Access to Eight-Port Expander Family
PART
I
2
C SLAVE
ADDRESS
INPUTS
INTERRUPT
MASK
OPEN-
DRAIN
OUTPUTS
PUSH-
PULL
OUTPUTS
I
2
C DATA WRITE I
2
C DATA READ
MAX7319 110xxxx 8 Yes — —
<I7–I0 interrupt
mask>
<I7–I0 port inputs>
<I7–I0 transition flags>
MAX7320 101xxxx — — — 8
<O7–O0 port
outputs>
<O7-O0 port inputs>
MAX7321 110xxxx Up to 8 — Up to 8 —
<P7–P0 port
outputs>
<P7–P0 port inputs>
<P7–P0 transition flags>
MAX7322 110xxxx 4 Yes — 4
<O7, O6 outputs,
I5–I2 interrupt
mask, O1, O0
outputs>
<O7, O6, I5–I2, O1, O0 port
inputs>
<0, 0, I5–I2 transition flags,
0, 0>
MAX7323 110xxxx Up to 4 — Up to 4 4 <port outputs>
<O7, O6, P5–P2, O1, O0 port
inputs>
<0, 0, P5–P2 transition flags,
0, 0>
MAX7328 0100xxx Up to 8 — Up to 8 —
<P7–P0 port
outputs>
<P7–P0 port inputs>
MAX7329 0111xxx Up to 8 — Up to 8 —
<P7–P0 port
outputs>
<P7–P0 port inputs>
www.maximintegrated.com
Maxim Integrated │ 7
MAX7321 I
2
C Port Expander with 8 Open-Drain I/Os