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1. Module-3
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2. • A control memory is a part of the control unit.
• Control Memory is the storage in the microprogrammed control unit
to store the microprogram.
• Any computer that involves microprogrammed control consists of
two memories.
• They are the main memory and the control memory.
• Programs are usually stored in the main memory by the users.
Whenever the programs change, the data is also modified in the
main memory.
• They consist of machine instructions and data.
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3. • The control memory consists of microprograms that are fixed
and cannot be modified frequently.
• They contain microinstructions that specify the internal control
signals required to execute register micro-operations.
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5. • The Control memory address register specifies the address of the
micro-instruction.
• The Control memory is assumed to be a ROM, within which all
control information is permanently stored.
• The control register holds the microinstruction fetched from the
memory.
• The micro-instruction contains a control word that specifies one or
more micro-operations for the data processor.
• While the micro-operations are being executed, the next address is
computed in the next address generator circuit and then transferred
into the control address register to read the next microinstruction.
• The next address generator is often referred to as a micro-program
sequencer, as it determines the address sequence that is read from
control memory.
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7. What is address sequencing in
computer architecture?
• Addressing sequence is able to increment the CAR (Control
address register).
• It provides the facility for subroutine calls and returns.
• A mappings process is provided by the addressing sequence from
the instructions bits to a control memory address.
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8. What is address sequencing in
microprogrammed control?
• Microinstructions are stored in control memory in groups, with
each group specifying a routine.
• Each computer instruction has its own microprogram routine in
control memory to generate the microoperations that execute the
instruction.
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11. Program Control Instructions
• A program control instruction changes address value in the PC and
hence the normal flow of execution.
• Change in PC causes a break in the execution of instructions.
• It is an important feature of the computers since it provides the control
over the flow of the program and provides the capability to branch to
different program segments.
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13. Typical Program Control Instructions
• Branch (BR) and Jump (JMP) instructions are used sometimes
interchangeably but, they are different.
• Branch and Jump instructions usually differ in addressing modes.
• Usually Jump is used to refer to unconditional version of branch.
• Skip (SKP) instructions is used to skip one(next) instruction.
• It can be conditional or unconditional. It does not need an address
field.
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14. • A conditional branch instruction is a branch instruction that may or
may not cause a transfer of control depending on the value of stored
bits in the PSR (processor status register).
• Each conditional branch instruction tests a different combination of
Status bits for a condition.
• If the condition is true, control is transferred to the effective address
(PC←Add). If the condition is false, the program continues with the
next instruction (PC←PC+1).
• Below is a list of Conditional Branch instructions, letter ‘N’ stands for
NOT.
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15. Conditional Branch Instructions
• ‘C’ represents the carry, or borrow after arithmetic addition or
subtraction.
• ‘N’ represents the leftmost bit of the result of the operation i.e. sign
bit.
• ‘V’ is for overflow i.e. if the sign of the result is changed (inverted).
• ‘Z’ is for zero i.e., to check whether the result of an operation is zero
(Z=1) or not zero (Z=0).
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17. • This mapping consists of placing a 0 in the most significant
bit of the address, transferring the four operation code bits,
and clearing the two least significant bits of the control
address register.
• This provides for each computer instruction a micro-program
routine with a capacity of four microinstructions.
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20. Subroutine
• A set of instructions that are used repeatedly in a program can be
referred to as Subroutine.
• Only one copy of this Instruction is stored in the memory. When a
Subroutine is required it can be called many times during the Execution
of a particular program.
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22. • Control Unit is the part of the computer's central processing unit
(CPU), which directs the operation of the processor.
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23. What are the characteristics of a control
unit?
• The control unit uses circuitry to control the actions of the processor.
• The control unit handles all input and output to and from the
processor.
• It interprets and executes instructions sequentially, guides data flow,
regulates and controls timing, and sends and receives control signals
from other devices.
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24. What is the purpose of control unit?
• The control unit controls and monitors communications between the
hardware attached to the computer.
• It controls the input and output of data, checks that signals have been
delivered successfully, and makes sure that data goes to the correct place
at the correct time.
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25. What is the control unit used for?
The Function of Control Unit
• It coordinates the flow of data out of, into, and between the various
subunits of a processor.
• It understands commands and instructions.
• It regulates the flow of data within the processor.
• It accepts external commands or instructions, which it turns into a series
of control signals.
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26. • CPU is the brain of the computer.
• All types of data processing operations and all the important functions of a
computer are performed by the CPU.
• It helps input and output devices to communicate with each other and perform
their respective operations.
• It also stores data which is input, intermediate results in between processing, and
instructions.
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27. What is CPU organization in computer
architecture?
CPU is organized with
• Program Counter (PC),
• Instruction Register (IR),
• Instruction Decoder,
• Control Unit,
• Arithmetic Logic Unit (ALU),
• Registers,
• Buses.
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28. What are 3 types of registers in CPU?
• memory address register (MAR)
• memory data register (MDR)
• current instruction register (CIR)
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29. Introduction:CPU
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33. • A register is a unique high-speed storage area in the CPU.
• Registers implement two important functions in the CPU operation:
• It can support a temporary storage location for data and fast access to
the data if required.
• It can save the status of the CPU and data about the implementing
program.
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34. Major Components of CPU:
1. Storage Components-register
2.Execution Components-ALU
3.Transfer Components-Bus
4.Control Components: Control Unit
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35. • Generally CPU has seven general registers.
• Register organization show how registers are selected and data flow
between register and ALU.
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37. Example:
• To perform the operation R3=R1+R2 We need to provide following
binary selection variable to the select inputs
• MUX A Selector( SELA): 001 –To place the contents of R1 into bus A
• MUX B Selector(SELB):010- To place the contents of R2 into bus B
• ALU operation Selector(OPR): To perform the arithmetic addition A+B
• Decoder Destination Selector(SEL D):011-To place the result available on
output bus in R3
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39. Control Word:
• The combined value of a binary selection inputs specifies the control
word.
• Control words for all micro operation are stored in the control
memory.
• It consist of four fields SELA, SELB, and SELD contains three bit each
and OPR field contains five bits.
• Therefore, the total bits in the control word are 14
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43. Example:
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