4-bit Adder-Subtractor Circuit
40 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the function of the mode input S in a 4-bit adder-subtractor circuit?

The mode input S controls whether the circuit performs addition (S = 0) or subtraction (S = 1).

How does the circuit perform subtraction when S = 1?

When S = 1, the circuit complements B and adds 1 through the input carry, effectively calculating A plus the 2's complement of B.

Describe the operation of a 4-bit binary incrementer.

A 4-bit binary incrementer adds one to the binary number in a register, using half-adders to propagate carries through the bits.

What is the purpose of half-adders in a 4-bit incremental circuit?

<p>Half-adders are used to add the least significant bit to a constant logic-1, enabling the increment operation.</p> Signup and view all the answers

Explain the role of multiplexers in a 4-bit arithmetic circuit.

<p>Multiplexers are used to select different arithmetic operations by controlling the data inputs to the adder component.</p> Signup and view all the answers

What is a circular shift and how does it differ from other types of shifts?

<p>A circular shift circulates bits around the two ends of the register without data loss, unlike other shifts that may lose information.</p> Signup and view all the answers

How is the output generated in a 4-bit binary incrementer?

<p>The output is generated by the final sum obtained from the cascading half-adders after adding one to the input value.</p> Signup and view all the answers

Describe the effect of an arithmetic shift-left operation on a signed binary number.

<p>An arithmetic shift-left multiplies a signed binary number by 2.</p> Signup and view all the answers

What is the significance of using a full-adder in the 4-bit adder-subtractor circuit?

<p>Full-adders are crucial for handling carry bits during the addition or subtraction operations, allowing for accurate multi-bit calculations.</p> Signup and view all the answers

What happens to a signed binary number during an arithmetic shift-right operation?

<p>An arithmetic shift-right divides the signed binary number by 2.</p> Signup and view all the answers

What happens to the input carry (C0) when performing subtraction in the adder-subtractor circuit?

<p>When performing subtraction, the input carry C0 is set to 1 to account for the addition of 1 while calculating 2's complement.</p> Signup and view all the answers

How is the sign bit affected by arithmetic shift operations?

<p>The sign bit remains unchanged during arithmetic shift operations.</p> Signup and view all the answers

In a combinational circuit shifter, what do the selection inputs determine?

<p>The selection inputs determine the direction of the shift operation, either left or right.</p> Signup and view all the answers

What are the required components for constructing a shifter with n data inputs and outputs?

<p>A shifter with n data inputs and outputs requires n multiplexers.</p> Signup and view all the answers

What is the primary function of the two serial inputs in the shifter design described?

<p>The two serial inputs are used to control the shift left and shift right operations.</p> Signup and view all the answers

Explain the term 'rotate operation' in the context of circular shifts.

<p>The term 'rotate operation' refers to the process of circularly shifting bits around the register, maintaining the data in a continuous loop.</p> Signup and view all the answers

What happens when timing signal T4 becomes active?

<p>The output of the AND gate for the control function D3D4 becomes active, which clears the sequence counter SC to 0 on the next positive clock transition.</p> Signup and view all the answers

Describe the four phases of an instruction cycle.

<p>The four phases are: Fetch an instruction from memory, Decode the instruction, Read the effective address from memory if necessary, and Execute the instruction.</p> Signup and view all the answers

What is the significance of the sequence counter SC in the instruction cycle?

<p>The sequence counter SC is incremented after each clock pulse to progress through the timing signals, ensuring the fetch and decode operations occur in sequence.</p> Signup and view all the answers

How is the instruction transferred from memory to the instruction register IR?

<p>The instruction is transferred during timing signal T1, where it is read into the instruction register IR while simultaneously incrementing the program counter PC.</p> Signup and view all the answers

Why is it necessary to transfer the address from PC to AR during timing signal T0?

<p>It is necessary because only AR is connected to the address inputs of memory, allowing the fetch operation to access the correct instruction.</p> Signup and view all the answers

What is the role of the AND gate in the control function of the sequence counter?

<p>The AND gate controls when the CLR input of SC is activated, dictating when the counter is cleared and transitioning the circuit based on timing signals.</p> Signup and view all the answers

Explain the purpose of decoding the instruction during the fetch and decode phases.

<p>Decoding the instruction is vital for determining the operation that needs to be executed and understanding any necessary addressing modes.</p> Signup and view all the answers

What condition causes the instruction cycle to stop?

<p>The instruction cycle stops when a HALT instruction is encountered, terminating the continuous execution of fetch-decode-execute cycles.</p> Signup and view all the answers

What is the role of the input flag FGI in the input-output configuration?

<p>The input flag FGI indicates whether new information is available in the input device; it is set to 1 when new information is present and cleared to 0 when the information is accepted by the computer.</p> Signup and view all the answers

Describe the sequence of events that occurs when a key is pressed on the keyboard.

<p>When a key is pressed, an 8-bit alphanumeric code is shifted into INPR, and the input flag FGI is set to 1 for the computer to process the input.</p> Signup and view all the answers

How does the computer determine when to transfer information from INPR to AC?

<p>The computer checks if the input flag FGI is set to 1; if it is, the information in INPR is transferred to AC, and FGI is cleared to 0.</p> Signup and view all the answers

What happens to the output flag FGO when the output device is busy printing?

<p>When the output device is busy, the output flag FGO is cleared to 0, indicating that it cannot accept new information until the current printing is completed.</p> Signup and view all the answers

Explain the significance of the 8-bit input register INPR.

<p>The 8-bit input register INPR holds alphanumeric input information that is received from the keyboard for processing by the computer.</p> Signup and view all the answers

What is the function of the output register OUTR in the output process?

<p>The output register OUTR receives encoded information from the accumulator (AC) for the output device to print.</p> Signup and view all the answers

What are input and output instructions used for in the context of the system described?

<p>Input and output instructions are necessary for transferring information to and from the AC register, checking flag bits, and controlling the interrupt facility.</p> Signup and view all the answers

How does the computer handle new information when the input flag FGI is cleared?

<p>When FGI is cleared to 0, the computer allows new information to be shifted into INPR by striking another key.</p> Signup and view all the answers

What role do the selection inputs S3S2 play in determining the type of operation in a digital system?

<p>The selection inputs S3S2 determine the type of operation by selecting between arithmetic, logic, and shift operations based on their binary values.</p> Signup and view all the answers

What is the significance of the stored program concept in general-purpose computers?

<p>The stored program concept allows computers to store instructions and data in memory, enabling them to execute a sequence of micro operations as defined by programs.</p> Signup and view all the answers

In the context of instruction codes, what does the operation part signify?

<p>The operation part of an instruction code signifies the specific operation to be performed, such as addition, subtraction, or shifting.</p> Signup and view all the answers

What happens to the input carry during logic operations as stated in the table?

<p>During logic operations, the input carry has no effect and is treated as a don't-care condition (marked with x's).</p> Signup and view all the answers

How does a computer execute an instruction read from memory?

<p>After reading an instruction from memory, the computer places it in a control register, which interprets the binary code and issues a sequence of micro operations to execute it.</p> Signup and view all the answers

What are instruction codes, and why are they important?

<p>Instruction codes are binary codes that specify a sequence of micro operations for the computer, and they are important because they define what actions the computer will perform.</p> Signup and view all the answers

Can all computers execute any operation without limitations, based on instruction codes?

<p>No, every computer has its own unique instruction set which defines the specific operations it can execute.</p> Signup and view all the answers

What is meant by micro operations in the context of computer instructions?

<p>Micro operations refer to the fundamental operations that a computer performs on data stored in its registers as specified by the instruction codes.</p> Signup and view all the answers

Study Notes

4-Bit Adder-Subtractor Circuit

  • Mode input S alters the function: S = 0 for addition, S = 1 for subtraction.
  • Exclusive-OR gates pair the input M with B; when S = 0, B remains unchanged; when S = 1, B's inputs are complemented.
  • When subtracting, input carry C0 is set to 1, facilitating the addition of 2's complement of B.

Binary Incrementer

  • The increment micro-operation increases a register’s value by one.
  • Example: A 4-bit register with binary 1101 increments to 1110.
  • Each half-adder in the increment circuit connects outputs, with the least significant half-adder receiving a constant logic-1 input.
  • Extending the design allows for n-bit incrementers with multiple half-adders.

Arithmetic Circuit

  • A composite circuit can perform various arithmetic micro-operations.
  • Basic structure includes parallel adder circuits and multiplexers for operation selection.
  • The circuit incorporates two 4-bit inputs (A and B) and one 4-bit output (D).

Circular Shift

  • Circular shifting rotates bits in a register without losing any information.
  • Outputs re-enter as inputs, allowing for continuous rotation in either direction.
  • Notation: cil for circular shift left, cir for circular shift right.

Arithmetic Shift

  • Arithmetic shifts adjust signed binary numbers—left shift multiplies by 2; right shift divides by 2.
  • The sign bit remains unchanged during shifts, preserving the number's sign.
  • A shifter designed with multiplexers caters to various shift operations and controls input direction.

Instruction Codes

  • Defines the sequence of micro-operations within a digital system.
  • Programs instruct the computer by dictating operations and operand sequences.
  • Binary instruction codes composed of operation parts specify actions like addition, subtraction, and shifts.
  • Each computer has a distinct instruction set based on the stored program concept.

Instruction Cycle

  • Comprises phases: fetching instructions from memory, decoding them, addressing, and executing.
  • Upon completion of execution, the process loops back to fetching the next instruction until a HALT instruction is encountered.

Fetch and Decode Phases

  • Program Counter (PC) loads the first instruction address.
  • Sequence Counter (SC) manages timing signals and increments after each clock pulse.
  • Micro-operations include transferring data to the Address Register (AR) and Instruction Register (IR) during specific timing signals.

Input-Output Configuration

  • Serial communication transfers data in 8-bit alphanumeric code.
  • The input interface transmits data from the keyboard to the Input Register (INPR).
  • An input flag (FGI) indicates new information availability; it signals data readiness to be transferred into the Accumulator (AC).

Information Transfer Process

  • Initially, FGI is cleared; when a key is pressed, data loads into INPR, setting FGI to 1.
  • If the flag is active, data transfers from INPR to AC in parallel, then FGI resets to 0 for new input.
  • Output process starts with the output flag (FGO) cleared; if FGO is active, data is sent from AC to Output Register (OUTR) for further processing.

Input-Output Instructions

  • Facilitate data transfer to/from the AC register, manage flag bits, and control interrupts.
  • Key for ensuring accurate input and output processing in the computing system.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

COA UNIT-I.pdf

Description

Explore the fundamentals of a 4-bit adder-subtractor circuit in this quiz. Understand how the mode input S controls the operation between addition and subtraction. Test your knowledge on how exclusive-OR gates and full-adders work in this context.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser