8085 architecture

8085 architecture

Acumulator:-It is a 8-bit register which is used to perform arithmetical and logical operation. It stores the output of any operation. It also works as registers for i/o accesses.

Temporary Register:-It is a 8-bit register which is used to hold the data on which the acumulator is computing operation. It is also called as operand register because it provides operands to ALU.

Registers:-These are general purposes registers. Microprocessor consists 6 general purpose registers of 8-bit each named as B,C,D,E,H and L.   Generally theses registers are not used for storing the data permanently. It carries the 8-bits data. These are used only during the execution of the instructions.
These registers can also be used to carry the 16 bits data by making the pair of 2 registers. The valid register pairs available are BC,DE HL. We cannot use other pairs except BC,DE and HL. These registers are programmed by user.


ALU:-ALU performs the arithmetic operations and logical operation.

Flag Registers:-It consists of 5 flip flop which changes its status according to the result stored in an accumulator. It is also known as status registers. It is connected to the ALU.
There are five flip-flops in the flag register are as follows:
1.Sign(S)
2.zero(z)
3.Auxiliary carry(AC)
4.Parity(P)
5.Carry(C)
The bit position of the flip flop in flag register is:           

                              

All of the three flip flop set and reset according to the stored result in the accumulator.
1.Sign- If D7 of the result is 1 then sign flag is set otherwise reset. As we know that a number on the D7 always desides the sign of the number.
if D7 is 1: the number is negative.
if D7 is 0: the number is positive.

2.Zeros(Z)-If the result stored in an accumulator is zero then this flip flop is set otherwise it is reset.

3.Auxiliary carry(AC)-If any carry goes from D3 to D4 in the output then it is set otherwise it is reset.

4.Parity(P)-If the no of 1's is even in the output stored in the accumulator then it is set otherwise it is reset for the odd.

5.Carry(C)-If the result stored in an accumulator generates a carry in its final output then it is set otherwise it is reset.

Instruction registers(IR):-It is a 8-bit register. When an instruction is fetched from memory then it is stored in this register.

Instruction Decoder:- Instruction decoder identifies the instructions. It takes the informations from instruction register and decodes the instruction to be performed.

Program Counter:-It is a 16 bit register used as memory pointer. It stores the memory address of the next instruction to be executed. So we can say that this register is used to sequencing the program. Generally the memory have 16 bit addresses so that it has 16 bit memory.
The program counter is set to 0000H.

Stack Pointer:-It is also a 16 bit register used as memory pointer. It points to the memory location called stack. Generally stack is a reserved portion of memory where information can be stores or taken back together.

Timing and Control Unit:-It provides timing and control signal to the microprocessor to perform the various operation.It has three control signal. It controls all external and internal circuits. It operates with reference to clock signal.It synchronizes all the data transfers.
There are three control signal:
1.ALE-Airthmetic Latch Enable, It provides control signal to synchronize the components of microprocessor.
2.RD- This is active low used for reading operation.
3.WR-This is active low used for writing operation.

There are three status signal used in microprocessor S0, S1 and IO/M. It changes its status according the provided input to these pins.
                               

Serial Input Output Control-There are two pins in this unit. This unit is used for serial data communication.

Interrupt Unit-There are 6 interrupt pins in this unit. Generally an external hardware is connected to these pins. These pins provide interrupt signal sent by external hardware to microprocessor and microprocessor sends acknowledgement for receiving the interrupt signal. Generally INTA is used for acknowledgement.

Hardware Interrupt:-
As i have already discussed that there are 6 interrupt pins in the microprocessor used as Hardware Interrupts given below:
TRAP
RST7.5
RST6.5
RST5.5
INTR
INTA is not an interrupt. INTA is used by the Microprocessor for sending
 the acknowledgement. TRAP has highest priority and RST7.5 has second highest priority and so on.

Difference between CISC and RISC Architecture

Difference between CISC and RISC Architecture

CISC | Complex instruction set Computing.

1.very large instruction sets reaching up to and above three hundred seperate instructions.

2. Performance was improved by allowing the simplification of program compilers, as the range of more advanced instructions available led to less refinements having to be made at the compilation process. However, the complexity of the processor hardware and architecture that resulted can cause such chips to be difficult to understand and program for, and also means they can be expensive to produce.

3. more specialized addressing modes and registers also being implemented, with variable length instruction codes.

4. Instruction pipelining can not be implemented easily.

5. Many complex instructions can access memory, such as direct addition between data in two memory locations. 

6. Mainly used in normal PC’s, Workstations and servers .

7. CISC systems shorten execution time by reducing the

number of instructions per program.

8. Examples of CISC Processors: Intel x86.

RISC | Reduced instruction set Computing.

1. Small set of instructions.

2. simplified and reduced instruction set, numbering one hundred instructions or less. because of simple instructions, RISC chips requires fewer transistors to produce processors. Also the reduced instruction set means that the processor can execute the instructions more quickly, potentially allowing for greater speeds. However, only allowing such simple instructions means a greater burden is placed upon the software itself. Less instructions in the instruction set means a greater emphasis on the efficient writing of software with the instructions that are available.

3. Addressing modes are simplified back to four or less, and the length of the codes is fixed in order to allow standardization across the instruction set.

4. Instruction pipelining can be implemented easily.

5. Only LOAD/STORE instructions can access memory.

6. Mainly used for real time applications.

7. RISC systems shorten execution time by reducing the clock

cycles per instruction (i.e. simple instructions take less time
to interpret).

8. Examples of RISC Processors: Atmel AVR, PIC, ARM.

Summary:

               CISC                                                                             RISC 

Large (100 to 300)                  Instruction Set                  Small (100 or less)

Complex (8 to 20)                  Addressing Modes                 Simple (4 or less) 

Specialized and complex         Instruction Format                               Simple

Variable                               Instruction Lengths                                Fixed

Variable                               Execution Cycles                  Standard for most

Higher                                 Cost / CPU Complexity                           Lower

Compilation                         Simplifies                              Processor design

Processor design                  Complicates                                      Software

Difficult                              Instruction Pipeline                                  Easy

POP3 Mail Vs Web-based E-mail

POP3 Mail Vs Web-based E-mail

1. POP3 Mail- Here to access the mail account user needs a „mail-client‟. A mail client is a simple application or program used entirely to receive and send mail. Internet Browsers Netscape and Internet explorer have e-mail clients included with them. But there are also stand alone e-mail clients such as Eudora which can be downloaded free from the internet. Web-based mail-This type of e-mail account is used by dozens of Internet service providers like Hotmail, yahoo etc.

2. POP3 Mail-The primary advantage of POP3 type email account is that it is usually not restrictive of the size of files which could be send or received. Web-based mail-The main disadvantage of this kind of account is the limited space in mail box and limited size of files that are allowed to send and receive.

3. POP3 mail-Most viruses are transmitted through this type of email. Many of the viruses are written to be specifically activated by usage of the e-mail client which comes with Internet explorer, outlook express. Web-based mail-Automatically prescans all the received attachment for viruses.

4. POP3 Mail-Filters are not easy to use here and spam is a problem here. Web-based mail-Filters are easy to use here to avoid spam.

5. POP3 mail-The account could be accessed only from the computer at which e-mail client is installed. Web-based mail-The account could be accessed from any computer having a web-browser.

6. POP3 mail-E-mail clients with POP connect to the server whenever the program starts and transfers all new messages to the local computer, thereby removing them from the server. Therefore server space is conserved here. Web-based mail-E-mails or messages remains on the server hence server space required is more.

7. POP3 mail-It makes the use of multiple computers very cumbersome and significantly reduces the security of the data. Web-based mail-If privacy and security are important web-based email service should be used.

PRESENTATION LAYER

                        It receives information from the application layer protocols and puts it into a format that all computers following the OSI model can understand.

                        It means that when a user constructs a word document in MS-word, while the receiver computer has only start office, so the receiver can’t open that file. But due to presentation layer he is able to open that.

                        It a user uses a Corel presentation to save a graphic, the presentation layer convert the graphic into a Tagged Image File Format (TIFF), Graphic Interchange Format (GYF) of Joint Photographic Experts Group (JPEG) format. This way if the user sends this graphic to another who does not have the Corel application the user’s O/S still present the graphic because it has been into a standard format. i.e it works as a TRANSPORT, which translates the format and application is using to a standard format used for passing manages over a network.

                                                The presentation layer negotiates and establishes the format the format in which data is exchanged. The main function performed by this layer are:-

        i.          A) Translation

     ii.            B)Encryption

   iii.            C)Decryption

   iv.            D)Data compression

     v.            E)Decompression

CHARACTERISTICS

·        Server as the interface between user application and the network.

·        Enables user application to interact with the network.

FOR REMEMBER:-

“PLEASE DO NOT THROUGH SU AZE PIZZA AWAY”

OR

“ALL PEOPLE SEEM TO NEED DATA POROCESING”

APPLICATION LAYER

It works closest to the user and provider file transmission , message exchange, terminal session and much more.

            The layer does not include the actual application, but includes the protocols that support the application. When an application needs to send data over the network, it passes instruction and the data to the protocols that support it at the application layer. Application layer send requests to an API, which is the door way to the supporting protocols. This layer process and property formats the data and passes it down to the next layer within the OSI model.

            Outlook                    Internet Explorer                         Printer

APPLICATION                   APPLICATION                               APPLICATION

 

SMPT

HTTP

LDP

EXAMPLES OF PROTOCOLS UNDER THIS LAYER:-

·        Simple mail transfer protocols (SMTP)

·        Hypertext transfer protocols(HTTP)

·        File transfer protocols(FTP)

·        Line printer daemon (LPD)

·        World wide web(WWW)

·        Talent

·        Trivial file transfer protocol (TETP)

·        Simple network management protocol (SNMP)

THE OSI MODEL

The OSI [open system interconnection] is a worldwide federation that works to provide international standard. It is standard description or “reference model” for how massage should be transmitted between any two points in a telecommunication network. It is an OSI standard for worldwide communications that defines a network for implementing protocols in seven layers. The OSI model does provide important guidelines that are used by vendors, engineers, developers and services into different layers. Each layer has its own responsibilities and functioning.

                        The OSI model was meant to help vendors create inter operable network devices, so that different vender’s network could work with each other. The OSI has seven different layers divided into group. The top 3 group defines how the application within the end stations will communicate each other and with users.

                                                                        The bottom 4 layers define how data is transmitted end to end.

NO.      LAYER                                    FEATURES SERVICES

7          APPLICATION                        FILE, MESSAGE DATABASE APPLICATION

6          PRESENTATION                    DATA ENCRYPTION, COMPRESSION, TRANSLATION

5          SESSION                                 DIALOUGE CONTROL

4          TRANSPORT                          END TO END CONNECTION

3          NETWORK                             ROUTING

2          DATALINK                             FRAMING

1          PHYSICAL                               PHYSISAL TOPOLOGY

                        The each protocol at specific OSI layer communication with a protocols that operates at the same OSI layer on another computer (end). This happens through encapsulation.

            A message is constructed at the application layer and then passed down through the protocol stack. Each layer adds its own information to the message thus the message grows in size as it goes down the protocol stack. The message is then sent to the destination computer and the encapsulation is reversed by taking the message apart through the same step as the source computer that encapsulation it.

By :-Krishna kumar