Transcript ch1603G1

16.1
THE CONTROL UNIT’S MICRO-OPERATIONS
By: MERLE SODEN
16.2
16.3
CONTROL OF THE PROCESSOR
By: YULEISYS TORRES
HARDWIRE IMPLEMENTATION
By: 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 “MicroOperations”.
 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
 Symbolic short hand
description of the moves.
 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).
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,
 Symbolic short hand
description of the moves.
 Once an instruction is
fetched, the next step is
to fetch the operands.
This creates more
operations and microoperations.
 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


Internally

Input that gives the status of system.
Outputs that allow it to manipulate the system.
The capabilities to perform sequencing and execution.
Three types of control signals:
1. Trigger ALU functions
2. Trigger a data path
3. External triggers (to bus or other external element)
Inputs:

Clock

Instruction Register (IR)


Flags
Control Signals from Control Bus
IR
Flags
•
•
•
Control signals
within CPU
Control
Unit
Control signals
from system bus
Clock
Outputs:

Control signals
to system bus
Control Signals to Control Bus
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.
Fetch
M
B
R
AC
PC
+1
IR
M•
A•
R•
ALU
Control
Unit
Control Signals
Control
Signals

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 Architecture
By: William Stallings(Preferred)
 Websites:
 www.wikipedia.org
 http://books.google.com/books?id=XaotdB-IekC&pg=PA182&lpg=PA182&dq=%22intel+pentium%22%22processor%22%22control+unit%22&s
ource=web&ots=ow69JFaU49&sig=XhLfi45L9ssxzgdd3nLFHLVye48&hl=en&sa=X&oi=book_result&re
snum=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=Mujt8KIAPYyyxs3e7CMfecf2F0&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=Mujt8KIAPYyyxs3e7CMfecf2F0&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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