The 74LS164 is an 8-bit edge-triggered shift register that accepts serial data input and converts it into parallel output. It has two serial input pins, DSA and DSB, which can be used interchangeably as a high-level enable to control the other input. These inputs should either be connected together or left tied high if not in use; they must never be left floating. The device also features an AND gate-enabled serial input and an asynchronous reset pin. The enable input helps suppress unwanted data signals by pulling them to a low level. When the reset signal is active (low), all outputs are set to a low state regardless of other inputs. Once the reset is released (high), the register shifts the input data bit by bit on each rising edge of the clock signal.
The 74LS164 offers several key features: it operates over a wide voltage range from 2V to 6V, can drive up to 10 LSTTL loads, and has a typical propagation delay of 20ns. At 5V operation, it provides ±4mA output current. It includes a buffer circuit for both the clock and serial input, and supports direct reset functionality. This makes it ideal for applications requiring simple serial-to-parallel conversion with minimal external components.
Pin Configuration and Functionality:
The 74LS164 comes in various packages, including DIP14, SO14, SSOP14, TSSOP14, and DHVQFN14. Each package has specific thermal characteristics, such as power dissipation limits decreasing linearly with temperature. For example, the DIP14 package loses 12mW per degree Celsius above 70°C, while the DHVQFN14 package loses 4.5mW per degree Celsius above 60°C.
Key Parameters:
- **Limit Parameters**: Maximum ratings for operating conditions.
- **Electrical Characteristics**: Includes supply voltage, input/output voltages, and current specifications.
- **Conversion Characteristics**: Describes the transition between logic levels.
- **Operating Range**: Defines the acceptable temperature and voltage ranges for reliable operation.
Logic Block Diagram and Timing:
The internal logic block diagram illustrates the structure of the shift register, including the flip-flops and control logic. The timing diagram shows the relationship between the clock, serial input, and output signals, ensuring proper synchronization during data shifting. Key timing requirements include setup and hold times, ensuring accurate data transfer and preventing errors during operation.
This IC is widely used in digital circuits for tasks like LED displays, data transmission, and signal processing. Its simplicity and reliability make it a popular choice for hobbyists and engineers alike. Whether you're building a basic project or designing a more complex system, the 74LS164 is a versatile and essential component.
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