The **PCF8564A** (specifically the 10-pin package variant) is a CMOS Real-Time Clock (RTC) and calendar optimized for low power consumption. It is frequently used in embedded systems to keep track of time even when the main microcontroller is powered down. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Interface** | I²C-bus (up to 400 kHz) | | **Supply Voltage** | 1.8V to 5.5V | | **Current Consumption** | Typ. 0.25 µA at 3.0V | | **Timekeeping** | Seconds, Minutes, Hours, Days, Weekdays, Months, Years | | **Clock Source** | 32.768 kHz Quartz Crystal | | **Package Options** | TSSOP10, HVSON10 | --- ### 2. Internal Functional Blocks The PCF8564A consists of several critical internal components: 1. **Oscillator Circuit**: Requires an external 32.768 kHz crystal. It provides the base frequency for timekeeping. 2. **Frequency Divider**: Reduces the 32 kHz signal down to 1 Hz to drive the clock counters. 3. **Registers**: A set of 8-bit registers (00h to 0Fh) that store time data, alarm settings, and control flags. 4. **Programmable Outputs**: Includes a clock output (`CLKOUT`) that can be set to different frequencies (e.g., 32.768 kHz, 1.024 kHz, 32 Hz, or 1 Hz). 5. **Interrupt Logic**: Triggers an output signal for alarms or timer overflows. --- ### 3. Pin Configuration (10-Pin Layout) The "10" in PCF8564A_10 typically refers to the 10-pin TSSOP or HVSON package. | Pin Number | Name | Description | | :--- | :--- | :--- | | 1 | **OSCI** | Oscillator Input (connects to crystal) | | 2 | **OSCO** | Oscillator Output (connects to crystal) | | 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 | | 8 | **VDD** | Power Supply (1.8V - 5.5V) | | 9/10 | **N.C.** | No Internal Connection (varies by specific sub-variant) | --- ### 4. Application Circuit Diagram (Concept) ```mermaid graph LR A[32.768kHz Crystal] --- B[PCF8564A] B --- C[I2C Bus: SDA/SCL] C --- D[Microcontroller] B --- E[Backup Battery/Supercap] E --- B ``` ### 5. Unique Features * **Century Flag**: Includes a bit to track century transitions, simplifying leap-year calculations up to the year 2099. * **Voltage Low Detector**: Features a flag that triggers if the supply voltage drops below a certain threshold, indicating that the time data may be invalid (e.g., battery failure). * **Alarm and Timer**: Supports daily/weekly alarms and a countdown timer for periodic wake-ups. ---