TCA6424 Datasheet, PDF (9/29 Pages) Texas Instruments – LOW-VOLTAGE 24-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS

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TCA6424
LOW-VOLTAGE 24-BIT I²C AND SMBus I/O EXPANDER
WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS
SCPS175 – NOVEMBER 2007
Register Descriptions
The Input Port registers (registers 0, 1 and 2) reflect the incoming logic levels of the pins, regardless of whether
the pin is defined as an input or an output by the Configuration register. They act only on read operation. Writes
to these registers have no effect. The default value (X) is determined by the externally applied logic level. Before
a read operation, a write transmission is sent with the command byte to indicate to the I²C device that the Input
Port register will be accessed next.
BIT
DEFAULT
BIT
DEFAULT
BIT
DEFAULT
Registers 0 and 1 (Input Port Registers)
I-07
I-06
I-05
I-04
I-03
I-02
I-01
I-00
X
X
X
X
X
X
X
X
I-17
I-16
I-15
I-14
I-13
I-12
I-11
I-10
X
X
X
X
X
X
X
X
I-27
I-26
I-25
I-24
I-23
I-22
I-21
I-20
X
X
X
X
X
X
X
X
The Output Port registers (registers 4, 5 and 6) shows the outgoing logic levels of the pins defined as outputs by
the Configuration register. Bit values in these registers have no effect on pins defined as inputs. In turn, reads
from these registers reflect the value that is in the flip-flop controlling the output selection, NOT the actual pin
value.
BIT
DEFAULT
BIT
DEFAULT
BIT
DEFAULT
Registers 2 and 3 (Output Port Registers)
O-07
1
O-17
1
O-27
1
O-06
1
O-16
1
O-26
1
O-05
1
O-15
1
O-25
1
O-04
1
O-14
1
O-24
1
O-03
1
O-13
1
O-23
1
O-02
1
O-12
1
O-22
1
O-01
1
O-11
1
O-21
1
O-00
1
O-10
1
O-20
1
The Polarity Inversion registers (registers 8, 9 and 10) allow polarity inversion of pins defined as inputs by the
Configuration register. If a bit in these registers is set (written with 1), the corresponding port pin's polarity is
inverted. If a bit in these registers is cleared (written with a 0), the corresponding port pin's original polarity is
retained.
BIT
DEFAULT
BIT
DEFAULT
BIT
DEFAULT
Registers 4 and 5 (Polarity Inversion Registers)
P-07
0
P-17
0
P-27
0
P-06
0
P-16
0
P-26
0
P-05
0
P-15
0
P-25
0
P-04
0
P-14
0
P-24
0
P-03
0
P-13
0
P-23
0
P-02
0
P-12
0
P-22
0
P-01
0
P-11
0
P-21
0
P-00
0
P-10
0
P-20
0
The Configuration registers (registers 12, 13 and 14) configure the direction of the I/O pins. If a bit in these
registers is set to 1, the corresponding port pin is enabled as an input with a high-impedance output driver. If a
bit in these registers is cleared to 0, the corresponding port pin is enabled as an output.
BIT
DEFAULT
BIT
DEFAULT
BIT
DEFAULT
Registers 6 and 7 (Configuration Registers)
C-07
1
C-17
1
C-27
1
C-06
1
C-16
1
C-26
1
C-05
1
C-15
1
C-25
1
C-04
1
C-14
1
C-24
1
C-03
1
C-13
1
C-23
1
C-02
1
C-12
1
C-22
1
C-01
1
C-11
1
C-21
1
C-00
1
C-10
1
C-20
1
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