<< Chapter < Page Chapter >> Page >

2.2 approach of hardwired logic

Principe:

- The Control Unit is viewed and designed as a combinatorial and sequential logic circuit.

- The Control Unit is implemented by using any of a variety of “standard” digital logic techniques. The logic circuit generate the fixed sequences of control signals

- This approach is used to generate fixed sequences of control signals with the higher speed.

Remarks:

  • The principle advantages are a high(er) speed operation and the smaller implementations (component counts)
  • The modifications to the design can be hard to do
  • This approach is favored in RISC style designs

3. microprogrammed control unit

The ideal of microprogrammed Control Unit is that the Control Unit design must include the logics for sequencing through micro-operations, for executing micro-operation, for executing micro-instructions, for interpreting opcodes and for making decision based on ALU flags. So the design is relatively inflexible. It is difficul to change the design if one wishes to add a new machine instruction.

The principal disadvantage of a microprogrammed control unit is that it will be slower than hardwired unit of comparable technology. Despite this, microprogramming is the dominant technique for implementing control unit in the contemporary CISC processor, due to its ease of implementation.

The control unit operates by performing consecutive control storage reads to generate the next set of control function outputs. Performing the series of control memory accesses is, in effect, executing a program for each instruction in the machine’s instruction set -- hence the term microprogramming.

The two basic tasks performed by a microprogrammed control unit are as follows:

- Micro-instruction sequencing: the microprogrammed control unit get the next mico-instruction from the control memory

- Micro-instruction execution: the microprogrammed control unit generate the control signals needed to execute the micro-instruction.

The control unit design must consider both affect the format of the micro-instruction and the timing of the control unit.

3.1 micro-instruction sequencing

Two problems are involved in the design of a micro-instruction sequencing technique is the size of micro-instruction and the address-generation time. The first concern is obvious minimizing the size of the control memory. The second concern is simply a desire to execute microinstruction as fast as possible.

In executing a microprogram, the address of the next microinstruction to be executed is one of these categories:

- Determined by instruction register

- Next sequential address

- Branch.

It is important to design compact time-efficient techniques for micro-instruction branching.

  • Sequencing technique

Three general categories for a control memory address are as follows:

- Two address fields

- Single address field

- Variable format

In Figure 7.3, the branch control logic with a single address field is illustrated.

Figure 7.3. Branch Control unit of Microprogrammed Control Unit with with a single address field

  • Address generation

The problem is to consider the various ways in which the next address can be derived or computed. The various techniques of the address generation is geven in the following.

Table 1: Microinstruction Address Generation techiques

3.2 micro-instruction execution

The microinstruction cycle is the basic event on a microprogrammed processor. Each cycle is made up the two parts: fetch and execute. This section deals with the execution of microinstruction. The effect of the execution of a microinstruction is to generate control signals for both the internal control to processor and the external control to processor.

A organization of a control unit is shown in Figure 7.4

Figure 7.4. Microprogrammed Control Unit Organization

4. classification of micro-instructions

Microinstruction can be classified in variety of ways in which the designer must choose the parallel “power” of each instruction. There are the following.

– Vertical microprogramming: Each microinstruction specifies a single (or few) microoperations to be performed

– Horizontal microprogramming: Each microinstruction specifies many different

microoperations to be performed in parallel.

  • Vertical microprogramming

– Width is narrow: n control signals can be encoded into log2n control bits

– Limited ability to express parallelism

– Considerable encoding of control information requires external memory word decoder to identify the exact control line being manipulated

  • Horizontal microprogramming

– Wide memory word

– High degree of parallel operations are possible

– Little to no encoding of control information

  • Compromise technique

– Divide control signals into disjoint groups

– Implement each group as a separate field in the memory word

– Supports reasonable levels of parallelism without too much complexity

  • Second compromise: nanoprogramming

– Use a 2-level control storage organization

– Top level is a vertical format memory

Output of the top level memory drives the address register of the bottom (nano-level) memory

– Nanomemory uses the horizontal formal. The produces the actual control signal outputs

– The advantage to this approach is significant saving in control memory size (bits)

– Disadvantage is more complexity and slower operation (doing 2 memory accesses fro each microinstruction).

  • Microprogramming applications

- For the typically large microprocessor systems today:

+ There are many instructions and associated register level hardware

+ There are many control point to be manipulated.

- Emulation

– The use of a microprogram on one machine to execute programs originally written to run on another machine.

– By changing the microcode of a machine, you can make it execute software from another machine.

Questions & Answers

how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Computer architecture' conversation and receive update notifications?

Ask