Understanding Shift Registers, Counters, and Logic Circuits

Posted on May 15, 2024 in Design and Engineering

Explain the Operation of a 4-Bit Parallel-In, Parallel-Out Shift Register with Data Input 1010

A 4-bit parallel-in, parallel-out shift register is a digital circuit that can store and shift a 4-bit binary number. In this type of shift register, data can be loaded into the register in parallel (all at once), and the stored data can be read out in parallel as well.

Let’s explain the operation using the given data input of “1010”:

1. Parallel Data Input (1010)

Initially, let’s assume all the flip-flops in the shift register are reset to 0. When the data input “1010” is applied in parallel to the four flip-flops (each flip-flop representing one bit), the respective values are loaded into the flip-flops. So, after loading, the state of the flip-flops would be: Q3 = 1, Q2 = 0, Q1 = 1, Q0 = 0.

2. Parallel Out

At this point, the stored data “1010” is available at the outputs of the flip-flops. Each flip-flop’s output represents one bit of the stored data. So, if we read the outputs in parallel, we would get the same data as the input: Q3 = 1, Q2 = 0, Q1 = 1, Q0 = 0.

3. Shift Operation

In a parallel-in, parallel-out shift register, there is no shifting of data involved. The data remains stored in the flip-flops until it is replaced by new input data. If we want to shift the data, we would use a different type of shift register, such as a parallel-in, serial-out shift register or a serial-in, serial-out shift register.

Difference Between Ring Counter and Johnson Counter

Ring Counter

  1. The output of the last flip-flop is connected back as the input to the starting flip-flop.
  2. The number of states in the ring counter is equal to the number of flip-flops used.
  3. The input frequency of the ring counter is ‘n’.
  4. The output frequency of the ring counter is ‘f/n’, where ‘f’ represents the input frequency.
  5. The total number of unused states in the ring counter is calculated as (2n – n), resulting in (n) unused states.

Johnson Counter

  1. The output of the last flip-flop is complemented and given as the input to the starting flip-flop.
  2. The number of states in the Johnson counter is double the number of flip-flops used, resulting in ‘2n’ states.
  3. The input frequency of the Johnson counter is ‘f’.
  4. The output frequency of the Johnson counter is ‘f/2n’.
  5. The total number of unused states in the Johnson counter is (2n – 2n), which means there are no unused states.

What is the Forbidden State in SR Flip-Flops?

In an SR flip-flop, the forbidden state refers to when both the Set (S) and Reset (R) inputs are active simultaneously. This state is not allowed because it leads to unpredictable behavior in the flip-flop.

Describe the Clocked Master-Slave J-K Flip-Flop with its Operational Table

  1. A clocked master-slave J-K flip-flop consists of two stages: a master stage and a slave stage. The flip-flop is controlled by a clock signal.
  2. Master Stage: This stage consists of two inputs – J (set) and K (reset). When the clock signal is high, the master stage takes the inputs and stores them temporarily.
  3. Slave Stage: This stage also has two inputs – J and K. It stores the output of the master stage. However, the inputs are only considered when the clock signal transitions from high to low (falling edge). This ensures that the output is stable and doesn’t change while the clock signal is high.

Define PLDs

PLD stands for Programmable Logic Device. It’s a type of digital logic device that can be programmed by the user to perform various logic functions. PLDs typically include programmable AND and OR arrays, along with programmable flip-flops or latches to store intermediate results.

Define Parallel Counter. Design MOD-12 Synchronous Up Counter Along with State Diagram, Timing Sequence, and Timing Diagram

A parallel counter is a digital circuit that counts in parallel by incrementing or decrementing a binary value using multiple flip-flops. Each flip-flop represents a bit in the counter, allowing for simultaneous updates of all bits. This design enables faster counting compared to serial counters.

Define Combination Logic Circuit. Design a Combination Circuit Whose Input is a Four-Bit Number and Whose Output is 1’s Complement of the Input Number

A combination logic circuit is a digital circuit that produces an output based solely on the current inputs, without regard to previous inputs. It operates using Boolean logic principles, combining inputs using logical operations such as AND, OR, and NOT gates to generate an output. These circuits are commonly used in various digital systems, including processors, memory units, and arithmetic units.

Define BCD Code. Design BCD to Excess-3 Code Converter with Truth Table and Logic Diagram

BCD stands for Binary Coded Decimal. It’s a binary representation of decimal numbers where each decimal digit is represented by its equivalent 4-bit binary number. In BCD, each decimal digit is represented by a unique 4-bit binary number, allowing easy conversion between binary and decimal representations. For example, the decimal number 5 is represented as 0101 in BCD. BCD is often used in digital systems for encoding decimal numbers for processing and display purposes.