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Figure 5: Program flow control without and with interrupts

The user program (depicted in figure 5a) performs a series of WRITE calls interleaved with processing. Code segments 1, 2, and 3 refer to sequences of instructions that do not involve I/O. The WRITE calls arc to an I/O program that is a System utility and that will perform the actual I/O operation. The I/O program consists of three sections:

  • A sequence of instructions, labeled 4 in the figure, to prepare for the actual I/O operation. This may include copying the data to be output into a special buffer and preparing the parameters for a device command.
  • The actual I/O command. Without the use of interrupts, once this command is issued, the program must wait for the I/O device to perform the requested func­tion (or periodically poll the device). The program might wail by simply repeat­edly performing a test operation to determine if the I/O operation is done.
  • A sequence of instructions, labeled 5 in the figure, to complete the operation. This may include setting a flag indicating the success or failure of the operation.

Because the I/O operation may lake a relatively long time to complete. The I/O program is hung up wailing for the operation to complete; hence. The user program is slopped at the point of the WRITE call for some considerable period of time

Interrupts and the instruction cycle

With interrupts, the processor can be engaged in executing other instructions while an I/O operation is in progress. Consider the flow of control in Figure 5b. As before, the user program reaches a point at which it makes a system call in the form of a WRITE call. The I/O program that is invoked in this case consists only of the preparation code and the actual I/O command. After these few instructions have been executed, control returns to the user program. Meanwhile, the external device is busy accepting data from computer memory and printing it. This I/O operation is conducted concurrently with the execution of instructions in the user program.

When the external device becomes ready to be serviced, that is, when it is ready to accept more data from the processor, the I/O module for that external device sends an interrupt request signal to the processor. The processor responds by suspending operation of the current program, branching off to a program to service that particular I/O device, known as an interrupt handler, and resuming the original execution after the device is serviced. The points at which such interrupts occur are indicated by an asterisk in Figure 5b.

From the point of view of the user program, an interrupt is just that: an interruption of the normal sequence of execution. When the interrupt processing is completed, execution resumes (Figure 6). Thus, the user program does not have to contain any special code to accommodate interrupts; the processor and the oper­ating system are responsible for suspending the user program and then resuming it at the same point.

Figure 6: The transfer of control via interrupt

Questions & Answers

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s. Reply
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s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
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SUYASH Reply
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SUYASH
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s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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Cied
types of nano material
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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many many of nanotubes
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what is the function of carbon nanotubes?
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I'm interested in nanotube
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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
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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
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name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
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silver nanoparticles could handle the job?
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this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
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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.
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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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