## PCA9536DG4: 4-Bit I2C and SMBus I/O Expander The **PCA9536DG4** is a CMOS device designed to provide remote I/O expansion for most microcontroller families via the I2C interface (Serial Clock - SCL, Serial Data - SDA). It is particularly useful when a design requires a few additional GPIO pins without moving to a larger, more expensive processor. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Number of I/Os** | 4 Bits | | **Interface** | I2C, SMBus | | **Supply Voltage (Vcc)** | 2.3V to 5.5V | | **Low Standby Current** | 1.0 $\mu$A (Typical) | | **Maximum Clock Frequency** | 400 kHz (Fast-mode) | | **Package** | SOIC-8 (The 'D' in the suffix) | | **Operating Temperature** | -40°C to 85°C | --- ### 2. Internal Register Structure The device is configured through four internal 8-bit registers. Since the device only has 4 I/O pins, only the lower 4 bits of these registers are functional. 1. **Input Port Register:** Reflects the incoming logic levels of the pins. 2. **Output Port Register:** Sets the outgoing logic levels when pins are defined as outputs. 3. **Polarity Inversion Register:** Allows the user to invert the polarity of the Input Port register data. 4. **Configuration Register:** Configures the direction of the I/O pins (0 = Output, 1 = Input). --- ### 3. Pin Configuration (SOIC-8) | Pin Number | Name | Description | | :--- | :--- | :--- | | 1 | **IO0** | Input/Output 0 | | 2 | **IO1** | Input/Output 1 | | 3 | **IO2** | Input/Output 2 | | 4 | **VSS** | Ground (0V) | | 5 | **IO3** | Input/Output 3 | | 6 | **SCL** | Serial Clock Line | | 7 | **SDA** | Serial Data Line | | 8 | **VCC** | Power Supply | --- ### 4. Hardware Implementation Notes * **I2C Addressing:** The PCA9536 has a **fixed** I2C address (`1000001` or `0x41` in 7-bit hex). Unlike other expanders, it does not have external address pins (A0, A1), meaning you can only have one PCA9536 on a single I2C bus. * **Pull-up Resistors:** External pull-up resistors are required on the SDA and SCL lines. * **Power-On Reset (POR):** When power is applied, an internal POR holds the device in its default state (all I/Os are configured as inputs). * **"G4" Suffix:** In Texas Instruments' nomenclature, the **G4** suffix signifies that the part is "Green" (Lead-Free and RoHS compliant), though it is functionally identical to the standard PCA9536D. --- ### 5. Application Code Example (Pseudocode) To set **IO0** as an output and drive it **High**: ```c // 1. Write to Configuration Register (0x03) // Set Bit 0 to '0' (Output), Bits 1-3 to '1' (Input) I2C_Write(0x41, 0x03, 0xFE); // 2. Write to Output Port Register (0x01) // Set Bit 0 to '1' (High) I2C_Write(0x41, 0x01, 0x01); ```