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MICRO COMPUTER SYSTEM DESIGN

MICRO COMPUTER SYSTEM DESIGN. MICROCOMPUTER

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MICRO COMPUTER SYSTEM DESIGN

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  1. MICRO COMPUTER SYSTEM DESIGN

  2. MICROCOMPUTER A digital system is defined by the registers it contains and the operation performed on the binary information stored in the registers. The number of distinct micro operations the required sequence of operations. The complexity of the design is in sequencing the operation to achieve the intended data processing task. The third alternative is to use a microcomputer to implement the digital system. INTRODUCTION

  3. A digital system can be constructed by means of MSI Circuits such as registers, decoders, ALU, memory and multiplexers. However a digital system constructed with MSI circuits would required a large number of IC package. Some digital systems are suitable for LSI design with component such as processer unit, microprogram sequencer, memory unit these systems can be microprogram to fit the required specfications. The microprogram LSI oragnization uses fewer ICs than the MSI implementation.

  4. MICROCOMPUTER Microcomputer systems are becoming very widely reed and find applications not only in the industry and laboratories, but also homes and offices. The basic structure of a microcomputer system is the same as that of a general purpose digital computer. • DISTRIPTION Advances in semiconductor technology have made available the entire CPU as a single Integrated Circuit (IC) called the Microprocessor. A computing system using a Microprocessor as a CPU is called a Microprocessor Based System or simply a Microcomputer system.

  5. Classification : • A microprocessor, which is a central processor unit (CPU) enclosed in one LSI packages. • Random-access memory (RAM) and read only memory (ROM) can be combined to form any memory size needed for an Application. • Programmeable interface units whose function is to interface between the CPU or memory and a wide.

  6. COMPONENTSOFMICROPROCESSOR Arithmetic Logic Unit (A LU). Registers. Control Unit. Input. Output. Memory. System Bus. Address Decoder.

  7. Arithmetic Logic Unit(A LU) : The ALU performs arithmetic operations such as addition,substraction and logic operations such as “AND”,”OR” and “Exclusive OR”. • REGISTERS : The registers are used for temporary storage of data during the execution of the program.Certain registers have special functions; for example holding the address of the next instruction to executed is one such function.

  8. INPUT : The purpose of input section is to accept data and program and transfer them to the cpu and memory. The most often used input device is a keyboard. Microprocessor based system generally use hexadecimal keyboard. The keyboard has 16 data keys from 0 to f, apart from some additional function keys. ex_ : analog to digital converters (ADC)

  9. OUTPUT : The result of computation prcessing inside the CPU are indicated to the outside world through the output devices. The commonly used output device is a serices of 7 segment display devices. Alternatively individual LEDs and relays can also be output devices.

  10. ADDRESS DECODER : To access a specific memory or I/O device the CPU puts its address on the address bus. However the address bys is common to all other memory devices and so the address reaches all other memory and I/O devices. Tomake only the specific memory device active, the address decoder circuit is used. It is designed to recognise the relevant device for a given address. It then selects the device through the enable signals. • SYSTEM BUS : Abus is a set of conductors carrying signals. It is called system bus since it serves the microcomputer system and is under its control.Thus the different units of the microprocessor system communicate through the system bus.

  11. Design : The microcomputer system may be divided into two parts: hardware design and software design. The Hardware design considers the inter connection of the physical components to provide a complete digital system. The software design is concerned with the development of the programs for a particular application. Writing programs for a microcomputer is essentially the same as a writing programs for any other computer the only difference is that a microcomputer programmer must be familiar with the hardware configuration and must take into consideration the problems associated with the particular application .

  12. MEMORY : Semiconductor memory devices are used to implement the memory. The memory device basically stores binary data zero or one. It will have provision to access an individual digit or a group of (4bit/8bit) digit together. A microprocessor based system will make use of a permanent memory device to store certain resident programs which are not changed during operation or even when power is turned off.These programs control the hardware and enable the user to enter and run his own program and data. Such programs are called Monitor programs.

  13. Memory Cycle : • The memory unit consists of both RAM and ROM. It is connected to the microprocessor through the address and data buses and the read and write control. • In the read cycle,the microprocessor places an address in ABUS and enables control line RD .The memory responds by reading the byte and placing it in DBUS. • In the write cycle, the microprocessor places an address in ABUS and a data byte in DBUS. At the same time, the control line WR is enabled.The memory responds toWR by writing the byte from DBUS into a memory location specified by the address in ABUS.

  14. “RAM“ & “ROM” A RAM chips is better suited for commumicating with a microprocessor if it has one or more inputs for selecting and enabling the unit only upon request. Another convenient feature is a bidirectional data bus to avoid inserting external bus buffers between the RAM and the data bus. The block diagram of a RAM chip suited for microprocessor applications .The capacity of the memory is 128 words of 8 bits each. This requires a 7-bit address and 8-bit bidirectional data bus. The read and write inputs are specify the memory operation and the two chip select (CS) control inputs are for enabling the chip only when it is selected by the microprocessor. The availabilty of more than one control input to select the chip facilitates the decoding of the address lines when multiple chips are used in the microcomputer.

  15. Features : The most important feature of the microcomputer is that a special purpose digital system having dedicated application can be designed by writing a program for a general purpose digital computer. The execution of the fixed, unalterable program causes the microcomputer to behave in a prescribed manner; just as a corresponding MSI-based digital system would behave. This method of digital design was not economically feasible to implement before the development of small, inexpensive microcomputer components.

  16. This permanent memory device is called Read Only Memory (ROM) because it is not possible to overwrite the contents of such a device. In addition , the microcomputer needs, some memory area for temporary storage of user’s program, intermediate data and results of computation. This read/write type temporary memory is called Random Access Memory (RAM).

  17. MICROCOMPUTER ORGANIZATION A typical microcomputer system consists of a microprocessor plus memory and I/O interface.The various components that form the system are linked through buses that transfer instars-actions, date, addresses and control information among the IC components . The purpose of the microprocessor is to provide a CPU whichinterprets instructions codes received from memory and to arithmetic, logic, and control operations on data stored in internal registers,memory words or interface units.

  18. The random access memory is a read-write memory type and consists of a number of IC packages connected together .The RAM is used to store data,variable parameters and intermediate results that need updating and are subject to change. The ROM consists of a number of IC packages and is used for storing programs and tables of constants that are not subject to change once the production of the microcomputer system is completed . The interface units provide the necessary paths for transferring information between the microprocessor and external input andoutput devices connected to I/O bus. This communication is specified by programmed instruction that direct data through the buses in the microcomputer system.

  19. The communication between the LSI components in a microcosm.takes place via the address and data buses. The data bus transfers data to and from the microprocessor and the memory or interface which is selected by the address bus.The data bus is bi-directional which means that the binary information can flow in either direction .A bi-directional,which means that the binary information can flow in either direction.A bi-directional data bus is used to save pins in the IC package. A set of separate data and address buses is the most common transfer path found in microprocessor. The advantage of this schema is that a microprocessor can select a word in memory and transfer the data word at the same time.

  20. Implied Mode : In this mode the operand is specified implicitly in the definition of the instruction. Instructions of this type are 1-byte instructions. For example the instruction “complement accumulator” is an implied-mode instruction because the operand in the accumulator register is implied in the definition of the instruction. • Register Mode : In this mode the operands are in registers which reside within the CPU. Register-mode instructions are 1-byte instructions and can be executed within the CPU without the need to reference memory for operands.

  21. Register-Indirect Mode : In this mode the instruction specifies a register or a pair of registers in the processor whose contents give the address of the operand in memory. Before using a register- indiredt mode instruction, the programmer must ensure that the address of the operand is placed in the processor register with a previous transfer- type instruction. • Immediate Mode : In this mode the operand is specified is the instruction itself. In an 8-bit microprocessor, the operand is placed in memory immediately after the operation-code byte. An immediate-mode instruction having an 8-bit operand is a 2-byte instruction.

  22. Direct-addressing Mode : In this mode the operand resides in memory and its address is given directly in the address part of the instruction. In 8-bit microprocessors with 16-bit addresses, a direct instruction consists of 3 bytes. Most direct – mode instructions assume that the other operands reside in processor registers. If more than one operand resides in memory, the instruction must include additional addresses to specify their locations. • Zero-page Addressing : This is similar to the direct-addressing mode except that the address part of the instruction contains only 1 byte. This is a 2-byte instruction, with the second byte specifying the 8 low-order bits of a memory address. The 8 high-order bits of the address are assumed to be all 0’s.

  23. Indexed Addressing : Instructions in this mode contain 3 bytes, with the last two giving a 16-bit address. The address part of the instruction is added to the value presently stored in the index register to obtain the effective address. The index register is often incremented or decremented to faciliatate the execution of program loops and to access tables of data stored in memory. • Base-register Addressing : This is similar to the indexed-addressing mode, except that the address part of the instruction consists of a number of bits that is less than the number of bits required for a full address. The register used in this mode is sometimes called a base register instead of an index register. The base register holds a base address, and the truncted address in the instruction specifies a displacement with respect to the base address.

  24. Indirect-Addressing : In this mode the address part of the instruction specifies the address where the effective address is stored. Control reads the address part of the instruction and uses it to address memory again to read the effective address. In a control-type instruction, the effective address is the branch address which is transferred to PC. • Indexed-indirect Addressing: This is an indirect-addressing mode ,except that the part of the instruction is added to the contents of the index register to determine the address where the effective address is stored in memory.

  25. Basic Set of Microprocessor Instructions • Microprocessor instructions may be classified in to three distinct types. 1.Transferinstructions that move data among registers, memory words ,and interface registers without changing the binary information content. 2.Operation instructions that perform operations on data stored in registers or memory words. 3.Control instructions used to test status conditions in registers and, depending on result, cause a change in program sequence.

  26. SUMMARY OF CONTENTS MICROCOMPUTER SYSTEM DESIGN • INTRODUCTION • MICROCOMPUTER ORGANIZATION • BUS BUFFER • MICROPROCESSOR ORGANIZATION • TYPICAL SET OF A CONTROL SIGNAL • MEMORY CYCLE • INSTRUCTIONS AND ADDRESSING MODES • STACK AND SUBROUTINE • MEMORY ORGANIZATION • INPUT OUTPUT INTERFACE

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