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The procedure mechanism involves two basic instructions: a call instruction that branches from the present location to the procedure, and a return instruction that returns from the procedure to the place from which it was called. Both of these are forms of branching instructions.

The above figure illustrates the use of procedures to construct a program. In this example, there is a main program starting at location 4000. This program includes a call to procedure PROC1, starting at location 4500. When this call instruction is encountered, the CPU suspends execution of the main program and begins ex­ecution of PROC1 by fetching the next instruction from location 4500. Within PROC1, there are two calls to PR0C2 at location 4800. In each case, the execution of PROC1 is suspended and PROC2 is executed. The RETURN statement causes the CPU to go back to the calling program and continue execution at the instruc­tion after the corresponding CALL instruction. This behavior is illustrated in the right of this figure.

Several points are worth noting:

1. A procedure can be called from more than one location.

2. A procedure call can appear in a procedure. This allows the nesting of proce­dures to an arbitrary depth.

3. Each procedure call is matched by a return in the called program.

Because we would like to be able to call a procedure from a variety of points, the CPU must somehow save the return address so that the return can take place appropriately. There are three common places for storing the return address:

• Register

• Start of called procedure

• Top of stack

4. addressing modes

The address field or fields in a typical instruction format are relatively small. We would like to be able to reference a large range of locations in main memory or for some systems, virtual memory. To achieve this objective, a variety of addressing techniques has been employed. They all involve some trade-off between address range and/or addressing flexibility, on the one hand, and the number of memory ref­erences and/or the complexity of address calculation, on the other. In this section, we examine the most common addressing techniques:

  • Immediate
  • Direct
  • Indirect
  • Register
  • Register indirect
  • Displacement

4.1 immediate addressing

The simplest form of addressing is immediate addressing, in which the operand is actually present in the instruction:

  • Operand is part of instruction
  • Operand = address field
  • e.g. ADD 5 ;Add 5 to contents of accumulator ;5 is operand

The advantage of immediate addressing is that no memory reference other than the instruction fetch is required to obtain the operand, thus saving one mem­ory or cache cycle in the instruction cycle.

The disadvantage is that the size of the number is restricted to the size of the address field, which, in most instruction sets, is small compared with the word length.

4.2 direct addressing

A very simple form of addressing is direct addressing, in which:

  • Address field contains address of operand
  • Effective address (EA) = address field (A)
  • e.g. ADD A ;Add contents of cell A to accumulator

The technique was common in earlier generations of computers but is not common on contemporary architectures. It requires only one memory reference and no spe­cial calculation. The obvious limitation is that it provides only a limited address space.

4.3 indirect addressing

With direct addressing, the length of the address field is usually less than the word length, thus limiting the address range. One solution is to have the address field refer to the address of a word in memory, which in turn contains a full-length address of the operand. This is known as indirect addressing.

4.4 register addressing

Register addressing is similar to direct addressing. The only difference is that the address field refers to a register rather than a main memory address.

The advantages of register addressing are that :

  • Only a small address field is needed in the instruction
  • No memory 'references are required, faster instruction fetch

The disadvantage of register addressing is that the address space is very limited.

4.5 register indirect addressing

Just as register addressing is analogous to direct addressing, register indirect ad­dressing is analogous to indirect addressing. In both cases, the only difference is whether the address field refers to a memory location or a register. Thus, for register indirect address: Operand is in memory cell pointed to by contents of register.

The advantages and limitations of register indirect addressing are basically the same as for indirect addressing. In both cases, the address space limitation (limited range of addresses) of the address field is overcome by having that field refer to a word-length location containing an address. In addition, register indirect addressing uses one less memory reference than indirect addressing.

4.6 displacement addressing

A very powerful mode of addressing combines the capabilities of direct addressing and register indirect addressing. It is known by a variety of names depending on the context of its use but the basic mechanism is the same. We will refer to this as displacement addressing, address field hold two values:

  • A = base value
  • R = register that holds displacement

Questions & Answers

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
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Sherica
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Sherica
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Tamia
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
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Rachael Reply
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Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
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
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
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
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Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
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