MAX7319 Maxim, MAX7319 Datasheet - Page 12

• Manufacturer Part Number: MAX7319
• Description: The MAX7319 2-wire serial-interfaced peripheral features eight input ports with selectable internal pullups, overvoltage protection to +6V, and transition detection with interrupt output
• Manufacturer: Maxim

I
Maskable Transition Detection
A write to the MAX7319 starts with the master transmit-
ting the MAX7319’s slave address with the R/W bit set
low. The MAX7319 acknowledges the slave address,
and samples the input ports during the acknowledge
bit. INT deasserts during the slave address acknowl-
edge. The master can now transmit 1 or more bytes of
data. The MAX7319 acknowledges these subsequent
bytes of data and updates the interrupt mask register
with each new byte until the master issues a STOP con-
dition (Figure 8).
The MAX7319 I
reset input RST, interrupt output INT, and the eight
input ports I0–I7 are overvoltage protected to +6V inde-
pendent of V+. This allows the MAX7319 to operate
from a lower supply voltage, such as +3.3V, while the
I
ven from a higher logic level, such as +5V.
The MAX7319 can operate from a higher supply volt-
age, such as +3V, while the I
of the input ports I0–I7 are driven from a lower logic
level, such as +2.5V. Apply a minimum voltage of 0.7 x
V+ to assert a logic-high on any input. For example, a
MAX7319 operating from a +5V supply may not recog-
nize a +3.3V nominal logic-high. One solution for input
level translation is to drive the MAX7319 inputs from
open-drain outputs. Use a pullup resistor to V+ or a
higher supply to ensure a high logic voltage of greater
than 0.7 x V+.
12
Figure 8. Writing to the MAX7319
2
2
C interface and/or any of the eight input ports are dri-
C Port Expander with Eight Inputs and
______________________________________________________________________________________
SDA
SCL
Port Input and I
Translation from Higher or Lower
START CONDITION
Applications Information
2
S
C interface (SDA, SCL, AD0, AD2),
1
2
SLAVE ADDRESS
3
4
2
Writing to the MAX7319
C interface and/or some
2
5
C Interface Level
6
Logic Voltages
7
R/W
8
0
A
DATA TO INTERRUPT MASK
DATA 1
RST, SCL, SDA, AD0, and AD2 remain high impedance
with up to +6V asserted on them when the MAX7319 is
powered down (V+ = 0). The MAX7319 can therefore
be used in hot-swap applications.
Each of the input ports I0–I7 has a protection diode to
GND (Figure 9). When a port input is driven to a voltage
lower than GND, the protection diode clamps the volt-
age to a diode drop below GND.
Each of the input ports I0–I7 also has a 40kΩ (typ)
pullup resistor that can be enabled or disabled. When a
port input is driven to a voltage higher than V+
body diode of the pullup enable switch conducts and
the 40kΩ pullup resistor is enabled. When the
MAX7319 is powered down (V+ = 0), every input port
appears as a 40kΩ resistor in series with a diode con-
nected to GND. Input ports are protected to +6V under
any of these circumstances (Figure 9).
Figure 9. Input Port Structure
S = START CONDITION
P = STOP CONDITION
t
PV
INPUT
ENABLE
PULLUP
A
DATA TO INTERRUPT MASK
V+
P
V+
DATA 2
SHADED = SLAVE TRANSMISSION
N = NOT ACKNOWLEDGE
40kΩ
MAX7319
t
PV
A
Hot Insertion
I0–I7
,
the