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PCA9538 Datasheet(PDF) 7 Page - Texas Instruments |
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PCA9538 Datasheet(HTML) 7 Page - Texas Instruments |
7 / 31 page Control Register and Command Byte 0 0 0 0 B1 B0 0 0 Register Descriptions PCA9538 www.ti.com ................................................................................................................................................ SCPS126E – SEPTEMBER 2006 – REVISED JUNE 2008 The last bit of the slave address defines the operation (read or write) to be performed. When it is high (1), a read is selected while a low (0) selects a write operation. Following the successful Acknowledgment of the address byte, the bus master sends a command byte that is stored in the control register in the PCA9538 (see Figure 5). Two bits of this command byte state the operation (read or write) and the internal register (input, output, polarity inversion or configuration) that will be affected. This register can be written or read through the I2C bus. The command byte is sent only during a write transmission. Once a command byte has been sent, the register that was addressed continues to be accessed by reads until a new command byte has been sent. Figure 5. Control Register Bits Command Byte Table CONTROL REGISTER BITS COMMAND BYTE REGISTER PROTOCOL POWER-UP DEFAULT (HEX) B1 B0 0 0 0x00 Input Port Read byte XXXX XXXX 0 1 0x01 Output Port Read/write byte 1111 1111 1 0 0x02 Polarity Inversion Read/write byte 0000 0000 1 1 0x03 Configuration Read/write byte 1111 1111 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 indicate to the I2C device that the Input Port register is accessed next. Register 0 (Input Port Register) Table 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) Table BIT O7 O6 O5 O4 O3 O2 O1 O0 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 polarity is inverted. If a bit in this register is cleared (written with a 0), the corresponding port pin original polarity is retained. Register 2 (Polarity Inversion Register) Table BIT N7 N6 N5 N4 N3 N2 N1 N0 DEFAULT 0 0 0 0 0 0 0 0 Copyright © 2006–2008, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Link(s): PCA9538 |
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