16.1 THE CONTROL UNIT’S MICRO-OPERATIONSBy: MERLE SODEN

16.2 CONTROL OF THE PROCESSORBy: YULEISYS TORRES

16.3 HARDWIRE IMPLEMENTATIONBy: LESTHER MARTI

In this presentation today I hope to give you a better understanding of what the term “micro-operations” means in the instruction cycle as it pertains to the

Control Unit.

We cannot begin a discussion about micro-operations of the CONTROL UNIT unless we first discuss the CONTROL UNIT itself.

If you don’t already know, the control unit is that portion of the CPU that actually initiates instructions.

It is similar to your brain creating a thought.

When I refer to the word INSTRUCTION, I am referring to a cycle of commands initiated by the CONTROL UNIT to carry out the thought of a user. The following are a list of instructions that you are already familiar with.

FETCH

INDIRECT

INTERRUPT

EXECUTE

INSTRUCTION

In each movement of the previous cycles (ie. Fetch…) the instructions are executed during an instruction cycle made up of shorter cycles.

Because the performance of each sub cycle involves one or more shorter operations we coin the term “Micro-Operations”.

As we already know the beginning of the instructions cycle starts with the FETCH CYCLE. Right?

Now you might be thinking to yourself, “Yeah, I already know about the fetch cycle, and the indirect cycle and the interrupt cycle and all that stuff right?”

And so you are also probably wondering what does that have to do with Micro Operations in the control unit right?

Well let me answer that for you.

Lets start with the FETCH CYCLE and see what happens there;

In the FETCH CYCLE, we know the following;

The address of the next instruction to be executed is in the program counter

The first step is to move that address to the memory address register (MAR),

The second step is to bring the address (in the MAR) and place it on the address bus.

(And don’t forget the PC will increment by 1 to get ready for the next instruction.)

At this time, the control unit issues a READ command on the control bus, and the result appears on the (MDR).

The last step is to move the contents of the MDR to the instruction register (IR).

Symbolic short hand description of the moves.

PC------MAR PC+1----PC RAM---MDR MDR---IR

- OR - t1: MAR (PC) t2: MBR Memory -PC (PC) + I t3: IR (MBR)

* Where the notation (t1, t2, t3) represents successive time units or clock pulses

As you can see, in the FETCH CYCLE, although there are three operations, there are actually four micro-operations, and each micro-operation involves the movement of data into or out of a register.

Let’s look at The Indirect Cycle it’s the same thing,

Once an instruction is fetched, the next step is to fetch the operands. This creates more operations and micro-operations.

Symbolic short hand description of the moves.

t1: MAR +- (IR(Address)) t2: MBR <— Memory t3: IR(Address) —

(MBR(Address))

Next let’s look at The Interrupt Cycle

At the completion of the execute cycle, a test is made to determine whether any enabled interrupts have occurred. If so, the interrupt cycle occurs.

Here are its Operations and micro-operations

Symbolic short hand description of the moves.

t1: MBR (PC) t2: MAR Save-address PC +- Routine-address t3: Memory +- (MBR)

Last but not least let’s look at The Execute Cycle.

First; consider an add instruction:

ADD R1, X

This particular case adds the contents of the location X to register R1. The following sequence of operations and micro-operations might occur:

Symbolic short hand description of the moves.

t1: MAR (IR(address)), t2: MBR Memory t3: RI- (RI) + (MBR)

In closing we have seen that each phase of the instruction cycle can be decomposed into a sequence of elementary movements called micro-operations.

Thank you.

The Control Unit is the engine that moves the computer.

It is the responsibility of the control unit to cause the execution of instructions.

Control Unit:

1.Basic elements of a processor.

2.Micro-operations that processor performs.

3.Functions that the control unit must perform to allow the

execution of the micro-operations.

The basic elements of a processor are:

1. The ALU

2. Registers

3. Internal data path

4. External data path

5. Control Unit

Micro-operations :

Transfer data between registers

Perform arithmetic or logical operations using registers as sources and as destinations for result.

Transfer data from outside the processor to a register.

Transfer data from a register to outside the processor.

The control unit performs two elementary tasks:

1. Sequencing

2. Execution

Control signals:

Externally Input that gives the status of system.

Outputs that allow it to manipulate the system.Internally

The capabilities to perform sequencing and execution.

Three types of control signals:

1.Trigger ALU functions2.Trigger a data path3.External triggers (to bus or other external element)

Inputs:

Clock

Instruction Register (IR)

Flags

Control Signals from Control BusControl

Unit

IRControl signals within CPU

Control signals to system bus

Control bus

Control signals from system bus

Clock

Flags• • •

Outputs:

Control Signals to Control Bus

Control Signals within processor

Control unit keeps track of what part in the instruction cycle it is currently in.

Fetch Cycle:1. Transfer contents of PC to MAR. 2. Read memory into the MBR and increment the PC.

End of Fetch Cycle:• Indirect cycle or execute cycle.

Control Unit

IR

Control Signals

• • •

PC

AC

MBR

MAR

ALUControl Signals

Fetch

+ 1

A single internal bus

Gates and control

Additional control signals

Two additional registers. Y and Z.

Register Z

In the Intel Pentium 4, which was introduced in 2000 is here Intel has redesigned their microprocessor architecture.

42 million transistors

Started new trend

Supports SSE3

FPU

SIMD (Single Instruction Multiple Data)

Additional MMX registers

Addditonal MMX Instruction code

The execution unit is capable of processing multiple instructions concurrently.

Simple integer processes performed and stored in the out-of-order area in C.U. until needed.

Complex integer and floating-point processes are streamlined.

Registers used as local storage.

Combinatorial circuit Type of logic circuit Input logic signals are transformed into a set of output

signals Control unit signals

Input signal Output signal

Control unit inputs– Instruction register – Flags– Controls bus signals– Clock

Instruction register

– Stores the instruction currently being executed

– Holds the instruction while it is being decoded

– Uses an op-code to perform different instructions

– Unique logic for each op-code

– Decoder takes encoded input and produces single

output

Flags– Status register – Contains current state of the processor – Stores binary values or codes– One or more bits – Each bit means something

Control bus signals– Wiring of the control unit– Communicates the CPU with other devices within

the computer– Differs from the Address and Data bus – Carries commands from the CPU and returns status

signals from the device

Clock– Controls the signals in the control unit during the

instruction cycle– Repetitive sequence of pulses– Measures the duration of micro-operations– Long periods to allow propagation of signals– Needs a counter with different control signals for

t1, t2 etc.

Complex sequencing & micro-operation logic Difficult to design and test Inflexible design Difficult to add new instructions

Book:

Computer Organization and ArchitectureBy: William Stallings(Preferred)

Websites:

www.wikipedia.org

http://books.google.com/books?id=XaotdB-I-ekC&pg=PA182&lpg=PA182&dq=%22intel+pentium%22%22processor%22%22control+unit%22&source=web&ots=ow69JFaU49&sig=XhLfi45L9ssxzgdd3nLFHLVye48&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA192,M1

http://books.google.com/books?id=ZFDqpSUPwAgC&pg=PA37&lpg=PA37&dq=%22intel+pentium%22%22processor%22%22control+unit%22&source=web&ots=X4O6XOoa7n&sig=Muj-t8KIAPYyyxs3e7CMfecf2F0&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA37,M1

http://books.google.com/books?id=ZFDqpSUPwAgC&pg=PA37&lpg=PA37&dq=%22intel+pentium%22%22processor%22%22control+unit%22&source=web&ots=X4O6XOoa7n&sig=Muj-t8KIAPYyyxs3e7CMfecf2F0&hl=en&sa=X&oi=book_result&resnum=10&ct=result#PPA38,M1

1. What are the two basic tasks of the control unit?

2. What provides the status of the processes?

3. What is used to transfer information in and out of the processor?

4. What is the importance of the control unit?

5. What is a micro-operation?

6. What cycle initiates the instruction cycle?

7. What are the four control unit inputs?

8. What does the control bus signal do?

9. What does the instruction register do?

10. What might possibly happen in each time cycle?

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