The **PCF8564AU** is a CMOS Real-Time Clock (RTC) and calendar optimized for low power consumption. It is commonly used in mobile devices, battery-powered systems, and industrial controllers to maintain accurate time even when the main system power is off. --- ### 1. Key Technical Specifications The PCF8564AU functions primarily as a peripheral device that communicates via the I²C-bus. | Feature | Specification | | :--- | :--- | | **Interface** | I²C-bus (up to 400 kHz) | | **Supply Voltage** | 1.8V to 5.5V | | **Current Consumption** | Typ. 0.25 µA (at VDD = 3.0V, 25°C) | | **Clock Output** | Programmable (32.768 kHz, 1.024 kHz, 32 Hz, 1 Hz) | | **Package** | TSSOP8 (indicated by the 'U' suffix) | --- ### 2. Functional Blocks The internal architecture consists of several critical electronic components: 1. **Oscillator Circuit:** Requires an external 32.768 kHz quartz crystal. It includes internal load capacitance, though external trimmers can be added for high-precision tuning. 2. **Frequency Divider:** Scales the 32.768 kHz signal down to 1 Hz to increment the seconds, minutes, hours, days, months, and years registers. 3. **Registers:** * **Time/Calendar:** Tracks seconds through years (including leap year compensation). * **Alarm:** Can be set to trigger an interrupt at a specific time. * **Control/Status:** Manages the operating mode and interrupt flags. 4. **Interrupt Generator:** An open-drain output (`/INT`) that can signal a host processor based on alarm events or timer overflows. --- ### 3. Pin Configuration (TSSOP8) The PCF8564AU is typically housed in an 8-pin package with the following layout: | Pin | Name | Description | | :--- | :--- | :--- | | 1 | **OSCI** | Oscillator Input | | 2 | **OSCO** | Oscillator Output | | 3 | **INT** | Interrupt Output (Active LOW, Open-drain) | | 4 | **VSS** | Ground (0V) | | 5 | **SDA** | I²C Serial Data Line | | 6 | **SCL** | I²C Serial Clock Line | | 7 | **CLKOUT** | Programmable Clock Output (Open-drain) | | 8 | **VDD** | Positive Supply Voltage | --- ### 4. Application Circuit Example To use the PCF8564AU, you need minimal external components: ```c // Typical Connection Logic - VDD: Connect to 3V battery or regulated 3.3V source. - SCL/SDA: Connect to MCU with 4.7k Ohm pull-up resistors. - OSCI/OSCO: Connect a 32.768 kHz crystal. - INT: Connect to an MCU GPIO with a pull-up resistor if alarms are needed. ``` --- ### 5. Notable Advantages * **Century Flag:** Unlike many older RTCs, it has a built-in flag to track century rollovers. * **Low Power:** Designed for "always-on" operation with minimal battery drain. * **Versatility:** The `CLKOUT` pin allows it to act as a precision frequency reference for other parts of the PCB.