TCA6408_09 Datasheet, PDF (9/31 Pages) Texas Instruments – LOW-VOLTAGE 8-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS

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TCA6408
LOW-VOLTAGE 8-BIT I²C AND SMBus I/O EXPANDER
WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS
SCPS151C – FEBRUARY 2007 – REVISED JUNE 2007
Register Descriptions
The input port register (register 0) reflects 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 this
register 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
Register 0 (Input Port Register)
I-7
I-6
I-5
I-4
I-3
I-2
I-1
I-0
X
X
X
X
X
X
X
X
The output port register (register 1) shows the outgoing logic levels of the pins defined as outputs by the
Configuration register. Bit values in this register have no effect on pins defined as inputs. In turn, reads from this
register reflect the value that is in the flip-flop controlling the output selection, not the actual pin value.
BIT
DEFAULT
Register 1 (Output Port Register)
O-7
O-6
O-5
O-4
O-3
O-2
O-1
O-0
1
1
1
1
1
1
1
1
The polarity inversion register (register 2) allows polarity inversion of pins defined as inputs by the configuration
register. If a bit in this register is set (written with 1), the corresponding port pin's polarity is inverted. If a bit in
this register is cleared (written with a 0), the corresponding port pin's original polarity is retained.
BIT
DEFAULT
Register 2 (Polarity Inversion Register)
N-7
N-6
N-5
N-4
N-3
N-2
N-1
N-0
0
0
0
0
0
0
0
0
The configuration register (register 3) configures the direction of the I/O pins. If a bit in this register is set to 1,
the corresponding port pin is enabled as an input with a high-impedance output driver. If a bit in this register is
cleared to 0, the corresponding port pin is enabled as an output.
BIT
DEFAULT
Register 3 (Configuration Register)
C-7
C-6
C-5
C-4
C-3
C-2
C-1
C-0
1
1
1
1
1
1
1
1
Power-On Reset
When power (from 0 V) is applied to V_CCP, an internal power-on reset holds the TCA6408 in a reset condition
until V_CCP has reached V_POR. At that time, the reset condition is released, and the TCA6408 registers and
I²C/SMBus state machine initialize to their default states. After that, V_CCP must be lowered to below 0.2 V and
back up to the operating voltage for a power-reset cycle.
Reset Input (RESET)
The RESET input can be asserted to intialize the system while keeping V_CCP at its operating level. A reset can
be accomplished by holding the RESET pin low for a minimum of t_W. The TCA6408 registers and I²C/SMBus
state machine are changed to their default state once RESET is low (0). When RESET is high (1), the I/O levels
at the P port can be changed externally or through the master. This input requires a pullup resistor to V_CCP, if no
active connection is used.
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