How Does PISO Shift Register Work?
To understand the operation of a PISO shift register, let’s consider a basic example with four flip-flops labeled D0, D1, D2, and D3. Each flip-flop can store one bit of data. The parallel data is loaded into the flip-flops simultaneously through the parallel input lines. Once the data is loaded, it can be shifted out in a sequential manner through the serial output.
4-bit PISO Shift Register Circuit Diagram:
To shift the data out, a clock signal is applied to the shift register. Each clock pulse triggers the movement of data from one flip-flop to the next in a cascading fashion. The most significant bit (MSB) is usually the first to be shifted out, followed by the remaining bits. The serial output provides the bits one at a time, in the order they were loaded.
Example:
Let us consider, We have a PISO shift register with four flip-flops (D0, D1, D2, and D3) and a 2-to-1 multiplexer. Initially, all flip-flops are cleared and contain the value ‘0’. We want to load the binary value ‘1010‘ into the shift register using parallel input and then shift the data out serially.
Solution:
Step 1: Parallel Input To load the value ‘1010’ into the shift register, we apply the parallel input as follows:
Data: 1 0 1 0
Step 2: Multiplexer Selection To facilitate the serial output, we use a 2-to-1 multiplexer. The inputs to the multiplexer are the outputs of the flip-flops (Q0, Q1, Q2, and Q3), and the select line of the multiplexer is controlled by the clock signal.
Initially, with the clock selecting the line at logic ‘0’, the multiplexer selects the first input (Q0) as the output.
Step 3: Clock Cycle (Shift Out) Now, we activate the clock signal to shift the data out serially. Each clock pulse triggers the movement of data from one flip-flop to the next, and the output of the multiplexer represents the serial data.
Clock Cycle 1:
Data Out: 1 (Q0)
Clock Cycle 2:
Data Out: 0 (Q1)
Clock Cycle 3:
Data Out: 1 (Q2)
Clock Cycle 4:
Data Out: 0 (Q3)
After four clock cycles, the binary value ‘1010‘ has been shifted out serially, with the MSB (Most Significant Bit) appearing first and the LSB (Least Significant Bit) appearing last.
In this numerical example, we demonstrated the operation of a 4-bit PISO shift register with the use of a multiplexer. We loaded the binary value ‘1010’ in parallel, and by applying clock cycles, we obtained the serial output ‘1010’ through the multiplexer. The combination of a PISO shift register and a multiplexer enables the efficient conversion of parallel data into a sequential, serial output, facilitating various applications such as data transmission, sensor systems, and more.
Parallel In Serial Out (PISO) Shift Register
Digital circuits play a vital role in processing and manipulating data efficiently. One important component of these circuits is a shift register, which allows data to be shifted in and out in a sequential manner. Among the various types of shift registers, the Parallel-In Serial-Out (PISO) shift register offers unique functionality that is valuable in many applications.