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  • First time unit: Move contents of PC to MAR.
  • Second time unit:
    • Move contents of memory location specified by MAR to MBR.
    • Increment by l the contents of the PC.
  • Third time unit: Move contents of MBR to IR.

Note that the second and third micro-operations both take place during the second time unit. The third micro-operation could have been grouped with the fourth with­out affecting the fetch operation:

t1: MAR<= (PC)

t2: MBR<= Memory

t3: PC<= (PC) + l

IR<= (MBR)

The groupings of micro-operations must follow two simple rules:

1. The proper sequence of events must be followed. Thus (MAR<= (PC)) must precede (MBR<= Memory) because the memory read operation makes use of the address in the MAR.

2. Conflicts must be avoided. One should not attempt to read to and write from the same register in one time unit, because the results would be unpredictable. For example, the micro-operations (MBR<= Memory) and (IR<= MBR) should not occur during the same time unit.

A final point worth noting is that one of the micro-operations involves an addi­tion. To avoid duplication of circuitry, this addition could be performed by the ALU. The use of the ALU may involve additional micro-operations, depending on the functionality of the ALU and the organization of the processor.

1.2 the indirect cycle

Once an instruction is fetched, the next step is to fetch source operands. Continuing our simple example, let us assume a one-address instruction format, with direct and indirect addressing allowed. If the instruction specifies an indirect address, then an indirect cycle must precede the execute cycle. The data flow includes the following micro-operations:

t1: MAR<= (IR (Address))

t2: MBR<= Memory

t3: IR(Address)<= (MBR(Address) )

The address field of the instruction is transferred to the MAR. This is then used to fetch the address of the operand. Finally, the address field of the IR is updated from the MBR, so that it now contains a direct rather than an indirect address.

The IR is now in the same state as if indirect addressing had not been used, and it is ready for the execute cycle. We skip that cycle for a moment, to consider the interrupt cycle.

1.3 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. The nature of this cycle varies greatly from one machine to another. We present a very simple sequence of events, we have

t1 : MBR<= (PC)

t2 : MAR<= Save_Address

PC<= Routine_Address

t3: Memory<= (MBR)

In the first step, the contents of the PC are transferred to the MBR, so that they can be saved for return from the interrupt. Then the MAR is loaded with the address at which the contents of the PC are to be saved, and the PC is loaded with the address of the start of the interrupt-processing routine. These two actions may each be a single micro-operation. However, because most processors provide multiple types and/or levels of interrupts, it may lake one or more additional micro-operations to obtain the save_address and the routine_address before they can be transferred to the MAR and PC, respectively. In any case, once this is done, the final step is to store the MBR, which contains the old value of the PC, into memory. The processor is now ready to begin the next instruction cycle.

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
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
what is system testing
what is the application of nanotechnology?
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
anybody can imagine what will be happen after 100 years from now in nano tech world
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
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit 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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