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PCA9557RGVR Datasheet(PDF) 8 Page - Texas Instruments |
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PCA9557RGVR Datasheet(HTML) 8 Page - Texas Instruments |
8 / 34 page Register Descriptions Power-On Reset RESET PCA9557 SCPS133I – DECEMBER 2005 – REVISED JUNE 2008.................................................................................................................................................... www.ti.com 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. It only acts 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 signal the I2C device that the input port register will be accessed next. Register 0 (Input Port Register) BIT I7 I6 I5 I4 I3 I2 I1 I0 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 O7 O6 O5 O4 O3 O2 O1 O0 DEFAULT 0 0 0 0 0 0 0 0 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 N7 N6 N5 N4 N3 N2 N1 N0 DEFAULT 1 1 1 1 0 0 0 0 The configuration register (register 3) configures the directions 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 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 C7 C6 C5 C4 C3 C2 C1 C0 DEFAULT 1 1 1 1 1 1 1 1 When power (from 0 V) is applied to VCC, an internal power-on reset holds the PCA9557 in a reset condition until VCC has reached VPOR. At that time, the reset condition is released, and the PCA9557 registers and I 2C/SMBus state machine initialize to their default states. After that, VCC 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 reset the system, while keeping the VCC at its operating level. A reset can be accomplished by holding the RESET pin low for a minimum of tW. The PCA9557 registers and I2C/SMBus state machine are held in their default states until RESET again is high. This input requires a pullup resistor to VCC if no active connection is used. 8 Submit Documentation Feedback Copyright © 2005–2008, Texas Instruments Incorporated Product Folder Link(s): PCA9557 |
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