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TCA6408PWRG4 Datasheet(PDF) 9 Page - Texas Instruments |
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TCA6408PWRG4 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 30 page www.ti.com Register Descriptions Power-On Reset Reset Input (RESET) TCA6408 LOW-VOLTAGE 8-BIT I2C AND SMBus I/O EXPANDER WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS SCPS151C – FEBRUARY 2007 – REVISED JUNE 2007 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. Register 0 (Input Port Register) BIT I-7 I-6 I-5 I-4 I-3 I-2 I-1 I-0 DEFAULT 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. Register 1 (Output Port Register) BIT O-7 O-6 O-5 O-4 O-3 O-2 O-1 O-0 DEFAULT 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. Register 2 (Polarity Inversion Register) BIT N-7 N-6 N-5 N-4 N-3 N-2 N-1 N-0 DEFAULT 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. Register 3 (Configuration Register) BIT C-7 C-6 C-5 C-4 C-3 C-2 C-1 C-0 DEFAULT 1 1 1 1 1 1 1 1 When power (from 0 V) is applied to VCCP, an internal power-on reset holds the TCA6408 in a reset condition until VCCP has reached VPOR. At that time, the reset condition is released, and the TCA6408 registers and I2C/SMBus state machine initialize to their default states. After that, VCCP must be lowered to below 0.2 V and back up to the operating voltage for a power-reset cycle. The RESET input can be asserted to intialize the system while keeping VCCP at its operating level. A reset can be accomplished by holding the RESET pin low for a minimum of tW. The TCA6408 registers and I 2C/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 VCCP, if no active connection is used. 9 Submit Documentation Feedback |
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