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What facts go into determining the use of the addressing bits of an instruction?
Almujahed
Following facts determine the use of addressing bits of an instruction: Number of addressing modes: Sometimes an addressing mode can be indicated implicitly. In other cases, the addressing modes must be explicit, and one or more mode bits will be needed. Number of operands: Typical instructions on today's machines provide for two operands. Each operand address in the instruction might require its own mode indicator, or the use of a mode indicator could be limited to just one of the address fields. Register versus memory: The more that registers can be used for operand references, the fewer bits are needed. Number of register sets: One advantage of using multiple register sets is that, for a fixed number of registers, a functional split requires fewer bits to be used in the instruction. Address range: For addresses that reference memory, the range of addresses that can be referenced is related to the number of address bits. Because this imposes a severe limitation, direct addressing is rarely used. With displacement addressing, the range is opened up to the length of the address register. Address granularity: In a system with 16- or 32-bit words, an address can reference a word or a byte at the designer's choice. Byte addressing is convenient for character manipulation but requires, for a fixed-size memory, more address bits.
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How many references are needed for each type of instruction to bring an operand into a processor?
Indirect addressing needs 2 reference to memory
How do you xxplain the types of memories?
Each instruction of a computer specifies an operation on certain data. The are various ways of specifying address of the data to be operated on. These different ways of specifying data are called the addressing modes. The most common addressing modes are:Immediate addressing modeDirect addressing modeIndirect addressing modeRegister addressing modeRegister indirect addressing modeDisplacement addressing modeStack addressing modeTo specify the addressing mode of an instruction several methods are used. Most often used are :a) Different operands will use different addressing modes.b) One or more bits in the instruction format can be used as mode field. The value of the mode field determines which addressing mode is to be used.The effective address will be either main memory address of a register.Immediate Addressing:This is the simplest form of addressing. Here, the operand is given in the instruction itself. This mode is used to define a constant or set initial values of variables. The advantage of this mode is that no memory reference other than instruction fetch is required to obtain operand. The disadvantage is that the size of the number is limited to the size of the address field, which most instruction sets is small compared to word length.INSTRUCTIONOPERANDDirect Addressing:In direct addressing mode, effective address of the operand is given in the address field of the instruction. It requires one memory reference to read the operand from the given location and provides only a limited address space. Length of the address field is usually less than the word length.Ex : Move P, Ro, Add Q, Ro P and Q are the address of operand.Indirect Addressing:Indirect addressing mode, the address field of the instruction refers to the address of a word in memory, which in turn contains the full length address of the operand. The advantage of this mode is that for the word length of N, an address space of 2N can be addressed. He disadvantage is that instruction execution requires two memory reference to fetch the operand Multilevel or cascaded indirect addressing can also be used.Register Addressing:Register addressing mode is similar to direct addressing. The only difference is that the address field of the instruction refers to a register rather than a memory location 3 or 4 bits are used as address field to reference 8 to 16 generate purpose registers. The advantages of register addressing are Small address field is needed in the instruction.
How many bits are needed for the program counter and the instruction register?
24 bits are needed for the program counter. Assuming the instructions are 32 bits, then 32 bits are needed for the instruction register.
The number of bits processed in a single instruction is known as?
8 Bits
Explain different types of addressing mode?
Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how machine language instructions in that architecture identify the operand (or operands) of each instruction. An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere.Number of addressing modesDifferent computer architectures vary greatly as to the number of addressing modes they provide in hardware. There are some benefits to eliminating complex addressing modes and using only one or a few simpler addressing modes, even though it requires a few extra instructions, and perhaps an extra register.[1] It has proven[citation needed] much easier to design pipelined CPUs if the only addressing modes available are simple ones. Most RISC machines have only about five simple addressing modes, while CISC machines such as the DEC VAX supermini have over a dozen addressing modes, some of which are quite complicated. The IBMSystem/360 mainframe had only three addressing modes; a few more have been added for the System/390.When there are only a few addressing modes, the particular addressing mode required is usually encoded within the instruction code (e.g. IBM System/390, most RISC). But when there are lots of addressing modes, a specific field is often set aside in the instruction to specify the addressing mode. The DEC VAX allowed multiple memory operands for almost all instructions, and so reserved the first few bits of each operand specifier to indicate the addressing mode for that particular operand. Keeping the addressing mode specifier bits separate from the opcode operation bits produces an orthogonal instruction set.Even on a computer with many addressing modes, measurements of actual programs[citation needed] indicate that the simple addressing modes listed below account for some 90% or more of all addressing modes used. Since most such measurements are based on code generated from high-level languages by compilers, this reflects to some extent the limitations of the compilers being used
Within a classful addressing subnet mask the bits indicate that corresponding bits in an IPv4 address contain network information?
the 1 bits
What addressing scheme was introduced in 1995 to resolve depletion of networking addresses by allowing for 128 bits to be used in addressing?
IPv6
What factor help in deciding the length of instruction format?
the number of bits required to represent an instruction of a cpu is known as length of the instruction or known as instruction.
Explain the different addressing method with an example each?
Each instruction of a computer specifies an operation on certain data. The are various ways of specifying address of the data to be operated on. These different ways of specifying data are called the addressing modes. The most common addressing modes are:Immediate addressing modeDirect addressing modeIndirect addressing modeRegister addressing modeRegister indirect addressing modeDisplacement addressing modeStack addressing modeTo specify the addressing mode of an instruction several methods are used. Most often used are :a) Different operands will use different addressing modes.b) One or more bits in the instruction format can be used as mode field. The value of the mode field determines which addressing mode is to be used.The effective address will be either main memory address of a register.Immediate Addressing:This is the simplest form of addressing. Here, the operand is given in the instruction itself. This mode is used to define a constant or set initial values of variables. The advantage of this mode is that no memory reference other than instruction fetch is required to obtain operand. The disadvantage is that the size of the number is limited to the size of the address field, which most instruction sets is small compared to word length.INSTRUCTIONOPERANDDirect Addressing:In direct addressing mode, effective address of the operand is given in the address field of the instruction. It requires one memory reference to read the operand from the given location and provides only a limited address space. Length of the address field is usually less than the word length.Ex : Move P, Ro, Add Q, Ro P and Q are the address of operand.Indirect Addressing:Indirect addressing mode, the address field of the instruction refers to the address of a word in memory, which in turn contains the full length address of the operand. The advantage of this mode is that for the word length of N, an address space of 2N can be addressed. He disadvantage is that instruction execution requires two memory reference to fetch the operand Multilevel or cascaded indirect addressing can also be used.Register Addressing:Register addressing mode is similar to direct addressing. The only difference is that the address field of the instruction refers to a register rather than a memory location 3 or 4 bits are used as address field to reference 8 to 16 generate purpose registers. The advantages of register addressing are Small address field is needed in the instruction.Register Indirect Addressing:This mode is similar to indirect addressing. The address field of the instruction refers to a register. The register contains the effective address of the operand. This mode uses one memory reference to obtain the operand. The address space is limited to the width of the registers available to store the effective address.Displacement Addressing:In displacement addressing mode there are 3 types of addressing mode. They are :1) Relative addressing2) Base register addressing3) Indexing addressing.This is a combination of direct addressing and register indirect addressing. The value contained in one address field. A is used directly and the other address refers to a register whose contents are added to A to produce the effective address.Stack Addressing:Stack is a linear array of locations referred to as last-in first out queue. The stack is a reserved block of location, appended or deleted only at the top of the stack. Stack pointer is a register which stores the address of top of stack location. This mode of addressing is also known as implicit addressing.Read more: http://wiki.answers.com/Explain_the_different_types_of_addressing_modes_in_8085_microprocessor.#ixzz1VB4Smbt3
What are the important instruction set design issues?
# Operation repertoire: How many and which operations to provide, and how complex operations should be # Data types: The various types of data upon which operations are performed # Instruction format: Instruction length (in bits), number of addresses, size of various fields, and so on. # Registers: Number of CPU registers that can be referenced by instructions, and their use. # Addressing: The mode or modes by which the address of an operand is specified
Difference between two address instruction and one address instruction?
Two address instructions use registers as operand locations.Example of a half word length (16 bit) Two address format.Bits 0-3 OP-Code bits (4 bits 16 different Mnemonics).Bit 4 instruction type ( e.g. 0 means half word length).Bit 5 fixed at value 1 used as extension to op-codes.Bits 6-9 Address A (4 bits refers to a registers hence a total of 16 registers).Bits 10-11 addressing modes ( 2 bits hence 4 different addressing modes in this case).Bits 12-15 Address B (4 bits refers to a registers hence a total of 16 registers).If 16 OP-codes for One address instructions is to be: ADD, ADC, SUB, SBC, XOR, BIT, CMP, INC, DEC, LDA, STA, AND, OR, JMP, BRN, JSR.For Two address instructions the following 6 OP-Codes are dropped: INC, DEC, STA, BRN, JMP, JSR, but new OP-Codes with the help of bit #5 is introduced instead------------------------------------------------now let's to introducingOne Address InstructionsThis is for a 32 bit CPU word length.Bits 0-3 OP Code bits (4 bits 16 different OP Codes).Bit 4 word length (0/1 Two different length 16 or 32 bit in this case).Bits 5-7 Addressing Modes (3 bits 8 different Addressing Modes).Bits 8-31 # of Addresses (2^24 Addressing Options).The possible OP-Codes could be: ADD, SUB, ADC, SBC, AND, XOR, ORA, BIT, CMP, LDA, STA, INC, DEC, BRN, JSR, JMP.one addressing24 bit Address3 bit AM1/0OP Codetwo addressing0000001111100010
What is the use of instruction decoder?
Instruction decoder takes bits stored in the instruction register and decodes it and tells to CPU what it need to do for it and enable the components for the operation. Simply, instruction decoder is like a dictionary. It tells the meaning of the instruction.
