The **74AHCT594S16-13** is a high-speed CMOS device featuring an 8-bit serial-in/parallel-out shift register with a storage register. It is commonly used for expanding output pins on microcontrollers. --- ### 1. Key Technical Specifications | Parameter | Specification | |:--- |:--- | | **Logic Family** | AHCT (Advanced High-Speed CMOS with TTL inputs) | | **Function** | 8-Bit Shift Register with Output Register | | **Voltage Supply Range** | 4.5V to 5.5V | | **Input Thresholds** | TTL Compatible (Low: 0.8V, High: 2.0V) | | **Output Current** | 8mA (Source/Sink) | | **Package Type** | SO-16 (Small Outline Package) | | **Operating Temp** | -40°C to +125°C | --- ### 2. Functional Components The device consists of two main internal stages: 1. **Shift Register:** Receives data serially (one bit at a time) via the `DS` pin on every rising edge of the shift clock (`SHCP`). 2. **Storage Register:** Also known as a "Latch." When the storage clock (`STCP`) pulses high, the data from the shift register is transferred to the parallel output pins ($Q_0$ to $Q_7$). --- ### 3. Pinout Description | Pin Name | Type | Description | |:--- |:--- |:--- | | **Q0 - Q7** | Output | 8-bit Parallel Outputs. | | **GND** | Ground | 0V Reference. | | **Q7S** | Output | Serial Output (for cascading multiple chips). | | **MR** | Input | Master Reset (Active Low) for the Shift Register. | | **SHCP** | Input | Shift Register Clock Input. | | **STCP** | Input | Storage Register (Latch) Clock Input. | | **SHR** | Input | Shift Register Reset (Active Low). | | **STR** | Input | Storage Register Reset (Active Low). | | **DS** | Input | Serial Data Input. | | **VCC** | Power | Positive Supply Voltage (5V). | --- ### 4. Implementation Example (Pseudo-code) To drive this chip using a microcontroller, you would typically use a "Bit-Banging" or SPI approach: ```cpp // Example: Sending the byte 0b10101010 void shiftOut(uint8_t data) { for (int i = 0; i < 8; i++) { // 1. Set Data Pin (DS) digitalWrite(DS_PIN, (data & (1 << i))); // 2. Pulse Shift Clock (SHCP) digitalWrite(SHCP_PIN, HIGH); digitalWrite(SHCP_PIN, LOW); } // 3. Pulse Latch Clock (STCP) to update physical outputs digitalWrite(STCP_PIN, HIGH); digitalWrite(STCP_PIN, LOW); } ``` --- ### 5. Why use "AHCT" vs "HC"? The "T" in AHCT indicates that the inputs are **TTL-level compatible**. This is crucial when interfacing a 5V shift register with a 3.3V microcontroller (like an ESP32 or STM32). A standard 74HC594 might not reliably detect 3.3V as a "High" logic level, whereas the 74AHCT594 will.