MAX7365 Maxim, MAX7365 Datasheet - Page 16

• Manufacturer Part Number: MAX7365
• Description: The MAX7365 is an I²C-interfaced peripheral that provides microprocessors with management of up to 56 key switches
• Manufacturer: Maxim

The device uses two techniques to minimize EMI radiat-
ing from the key-switch wiring. First, the voltage across
the switch matrix never exceeds 0.5V if not in sleep
mode, independent of supply voltage V
the voltage swing at any node when a switch is pressed
to 0.5V (max). Second, the keys are not dynamically
scanned, which would cause the key-switch wiring to
continuously radiate interference. Instead, the keys are
monitored for current draw (only occurs when pressed),
and debounce circuitry only operates when one or more
keys are actually pressed.
The device is designed to be insensitive to resistance,
either in the key switches, or the switch routing to and
Table 6. Keys FIFO Register (0x00)
General bit description
Key number indicated by D[5:0] is a keypress. Last
data in the FIFO.
Key number indicated by D[5:0] is a keypress. More
data in the FIFO.
Key number indicated by D[5:0] is a key release. Last
data in the FIFO.
Key number indicated by D[5:0] is a key release. More
data in the FIFO.
FIFO is empty.
FIFO is overflowed. Continued to read data in the FIFO.
Key repeat. Indicates the last data in the FIFO.
Key repeat. Indicates more data in the FIFO.
SPECIAL FUNCTION
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Switch On-Resistance
Key-Switch Controller with GPIO Ports
Low-EMI Operation
DD
. This reduces
FIFO not-empty
flag
D7
0
1
0
1
0
0
0
0
1MHz I
from the appropriate COL_ and ROW_ up to 5kI (max).
These controllers are therefore compatible with low-cost
membrane and conductive carbon switches.
The INT, SCL, and SDA remain high impedance with up
to 3.6V asserted on them when the device powers down
(V
4V asserted on them when not powered. The device can
be used in hot-swap applications.
The device operates with a 1.62V to 3.6V power-supply
voltage. Bypass the power supply (V
0.1FF or higher ceramic capacitor as close as possible
to the device.
DD
= 0V). I/O ports remain high impedance with up to
Key-release
KEYS FIFO REGISTER DATA
flag
D6
0
0
1
1
0
1
0
1
2
C-Interfaced 8 x 7
Power-Supply Considerations
D5
X
X
X
X
1
1
1
1
Key number/Key event
D4
X
X
X
X
1
1
1
1
Register Tables
D3
MAX7365
X
X
X
X
1
1
1
1
DD
Hot Insertion
) to GND with a
D2
X
X
X
X
1
1
1
1
D1
X
X
X
X
1
1
1
1
D0
X
X
X
X
1
1
0
0