The 74LS164 is an 8-bit serial-in, parallel-out shift register. It allows data to be input serially through one of two inputs (DSA or DSB) and then output in parallel across eight output pins. This makes it ideal for applications where data needs to be converted from a serial format to a parallel one, such as driving LED displays or other digital devices.
The two data inputs (DSA and DSB) can be used interchangeably. They are typically connected together or the unused input is tied high. It's important not to leave any input floating, as this could lead to unstable behavior. The device also features an enable control input that can suppress unwanted data by holding it at a low level, ensuring only valid data is shifted into the register.
Additionally, the 74LS164 includes an asynchronous reset (MR) input. When this pin is pulled low, all outputs are immediately set to a low state, regardless of the current state of the register or clock signal. This allows for quick and reliable clearing of the register without waiting for a clock cycle.
Each time the clock (CP) signal transitions from low to high, the data is shifted one bit to the right. The first bit of data is loaded into Q0, which is the result of the logical AND of the two data inputs (DSA and DSB). The setup time before the rising edge of the clock must be sufficient to ensure proper operation.
The internal circuitry of the 74LS164 includes a series of flip-flops connected in a cascade, with each stage receiving the output of the previous one. This configuration allows for sequential shifting of data through the register. A truth table and logic diagram provide further insight into how the device operates under different input conditions.
Overall, the 74LS164 is a versatile and widely used component in digital electronics, offering a simple yet effective way to handle serial-to-parallel data conversion. Its ease of use, combined with its reliability, makes it a popular choice in many digital circuits.
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