Microprocessor Instruction Set Quiz

Questions and Answers

What is the first step in executing an instruction like ADD (R3), R1?

Perform the addition

Load the result into R1

Fetch the first operand from memory

Fetch the instruction (correct)

Which control sequence corresponds to an unconditional branch operation?

PCout, MARin, Read, Select

MDRout, IRin

Zout, PCin, Yin, WMFC

PCout, PCin, Yin, WMFC (correct)

In a single-bus organization, what is a disadvantage related to the control sequence during execution?

Fewer clock cycles are required

More data can be transferred simultaneously

Only one data item can be transferred at a time (correct)

Instructions execute faster

What operation follows the fetching of MDRout and IRin in the execution sequence of ADD (R3), R1?

R3out, MARin, Read Signup and view all the answers

What does the control sequence 'Zout, R1 in, End' achieve in the context of executing instructions?

Ends the instruction execution process Signup and view all the answers

What happens to the microprogram counter (μPC) when a branch instruction is encountered and its condition is satisfied?

It is loaded with the branch address. Signup and view all the answers

What is one characteristic of a multiple-bus organization compared to a single-bus organization?

It reduces the number of required clock cycles for execution Signup and view all the answers

How is the transformation of instruction code bits into an address in control memory referred to?

Mapping process Signup and view all the answers

In a three bus organization, what is the primary function of the incrementer?

To update the program counter Signup and view all the answers

Which of the following statements is true about the ability to handle complex instructions in Hardwired versus Microprogrammed control?

Hardwired control handles complex instructions more easily than Microprogrammed control. Signup and view all the answers

What is a key characteristic of Horizontal Microprogramming?

Enables maximum parallelism with multiple signals simultaneously. Signup and view all the answers

Which components are combined into a single block referred to as the register file?

All general-purpose registers Signup and view all the answers

In terms of the design process, which of the following describes Hardwired control compared to Microprogrammed control?

Complicated for Hardwired control and simpler for Microprogrammed control. Signup and view all the answers

What is the typical range of ROM size for a Microprogrammed control unit?

Between 2k to 10k bits Signup and view all the answers

Which type of processor typically utilizes Microprogrammed control?

CISC processors Signup and view all the answers

What is one disadvantage of Microprogrammed control compared to Hardwired control?

Lower processing speed Signup and view all the answers

What is the role of the control step counter in the control unit design?

It keeps track of the control steps during instruction execution. Signup and view all the answers

Which component is responsible for decoding the instruction loaded in the Instruction Register (IR)?

Instruction decoder Signup and view all the answers

How does the encoder generate control signals?

By using inputs from various sources such as the instruction decoder and external inputs. Signup and view all the answers

What happens at the end of instruction execution in relation to the control step counter?

It resets and prepares for the next instruction. Signup and view all the answers

Which information is NOT used to determine the required control signals?

Timing information from the clock Signup and view all the answers

What is the purpose of the step decoder in the hardwired control unit?

To provide a separate signal line for each control sequence step. Signup and view all the answers

Which of the following conditions must be met for an instruction to be executed completely?

Each control step is completed in one clock period. Signup and view all the answers

What is the relationship between the control signals and the instruction execution?

Control signals direct the operations performed during instruction execution. Signup and view all the answers

What is the formula to calculate the speed up of a K-stage pipeline over a non-pipelined processor?

S = (time without pipeline) / (time with pipeline) Signup and view all the answers

As the number of tasks increases, what does the expression K + n - 1 approach?

n Signup and view all the answers

What is the maximum speed up that can be achieved in a pipelined processor?

K Signup and view all the answers

How is the efficiency of a pipeline defined?

E = speed up factor / number of stages Signup and view all the answers

What does throughput refer to in the context of a pipeline?

The number of tasks completed per unit time Signup and view all the answers

In cases of large numbers of tasks, how is speed up expressed as a function of K?

S = K Signup and view all the answers

What is the relationship between tn and tp in a non-pipelined processor?

tn = K * tp Signup and view all the answers

Which equation accurately expresses efficiency in a K-stage pipeline?

E = (n * K) / (K + (n - 1)) Signup and view all the answers

What information does the CPU send to initialize the DMA?

Starting address, word count, transfer mode, and control signal Signup and view all the answers

What signal does the DMA controller send to inform the CPU to stop bus communication?

BR line Signup and view all the answers

What happens when the CPU's BG line is high?

DMA uses RD and WR lines for read/write Signup and view all the answers

Which of the following statements is true regarding DMA transfer initiation?

The CPU stops communication until an interrupt signal is received Signup and view all the answers

What is the role of the DMA acknowledge signal in the process?

To coordinate start of data transfer with peripheral device Signup and view all the answers

What is transmitted by the device when it receives a DMA acknowledge?

A word onto the data bus for writing Signup and view all the answers

What does the CPU do after initializing the DMA?

Waits for an interrupt signal Signup and view all the answers

What function does the control of transfer mode serve in DMA initialization?

Decides whether to read or write data Signup and view all the answers

Study Notes

Branch Instructions and Micro Program Control

When a branch instruction meets its conditions, the micro Program Counter (μPC) updates to the branch address.
An END instruction causes the μPC to load the address of the first memory word.
In other cases, the μPC increments with each new micro instruction fetched.

Mapping Process

Transformation of instruction code to a control memory address is known as the Mapping process.
The basic microinstruction format includes fields: F1, F2, F3 (function fields), CD (condition field), BR (branch field), and Address.

Comparison: Hardwired vs Microprogrammed Control

Hardwired control is faster, while microprogrammed control is slower.
Hardwired functions are implemented in hardware; microprogrammed functions utilize software.
Hardwired control handles complex instructions, whereas microprogrammed control simplifies complexity.
Hardwired design is complicated compared to the systematic nature of microprogrammed design.
Instruction set size varies, with hardwired under 100 instructions and microprogrammed over 100.
ROM size for hardwired control is non-existent, whereas microprogrammed control uses 2k to 10k bits.
Applications: Hardwired in RISC processors, microprogrammed in CISC and mainframes.

Horizontal Microprogramming

Allows maximum parallelism as one bit is assigned per control signal.
Requires no additional decoders; however, larger control word lengths increase memory access frequency.
Control sequence for unconditional branching includes several PC and WMFC operations.

Execution of Complete Instruction

Fetching and executing an instruction as in ADD (R3), R1 involves multiple steps: fetching instruction, obtaining operand at R3, performing addition, and loading result into R1.
Control sequence for the execution in a single-bus organization spans several detailed operations that include reading from memory and transferring results.

Multiple-Bus Organization

Single bus structures lead to lengthy control sequences as only one data item transfers per cycle.
Commercial processors often have multiple internal paths for parallel data transfers.
Three-bus organization enhances data transfer efficiency.

Hardwired Control Unit Design

Comprises a control step counter and step decoder to manage control signals.
Required control signals are established based on internal registers, condition flags, and external inputs.
Each instruction execution step aligns with a clock period.

DMA Transfer Process

Direct Memory Access (DMA) requires initialization by the CPU: specifying memory block address, word count, transfer control, and starting DMA.
Upon receiving a DMA request, the DMA controller informs the CPU to relinquish bus control and initiates reading or writing processes.

Pipeline Speed-Up Ratio

Speed-up (S) of a K-stage pipeline over a non-pipelined equivalent is determined by comparing execution times.
As task count increases, speed-up approaches K, the number of pipeline stages.
The maximum theoretical speed-up achievable in a pipelined processor equals the number of stages (K).

Pipeline Efficiency and Throughput

Efficiency (E) of a pipeline is defined as the speed-up factor divided by the number of stages.
Throughput refers to the number of tasks a pipeline can complete per unit time, indicating overall system performance.

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Description

Test your knowledge on microprocessor branch instructions and their behaviors. This quiz will cover the loading of the microprogram counter (µPC) upon encountering various instructions like branch and END. Answer questions about instruction execution flow and the effects on memory addressing.