Supported types are marked with DATA TYPES ON THE ULTRASPARC III The 8051

Supported types are marked with data types on the

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Supported types are marked with ×. DATA TYPES ON THE ULTRASPARC III
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The 8051 numeric data types. Supported types are marked with ×. DATA TYPES ON THE 8051
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An instruction consists of an opcode, usually along with some additional information such as where operands come from, and where results go to. The general subject of specifying where the operands are (i.e., their addresses) is called addressing. Instructions always have an opcode to tell what the instruction does. There can be zero, one, two, or three addresses present. INSTRUCTION FORMATS
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Four common instruction formats: (a) Zero-address instruction. (b) One-address instruction (c) Two-address instruction. (d) Three-address instruction. INSTRUCTION FORMATS
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On some machines, all instructions have the same length; on others there may be many different lengths. Instructions may be shorter than, the same length as, or longer than the word length. Having all the instructions be the same length is simpler and makes decoding easier but often wastes space, since all instructions then have to be as long as the longest one. INSTRUCTION FORMATS
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Some possible relationships between instruction and word length. INSTRUCTION FORMATS
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When a computer design team has to choose instruction formats for its machine, they must consider a number of factors. The difficulty of this decision should not be underestimated. The decision about the instruction format must be made early in the design of a new computer. DESIGN CRITERIA FOR INSTRUCTION FORMATS
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If the computer is commercially successful, the instruction set may survive for 20 years or more. The ability to add new instructions and exploit other opportunities that arise over an extended period are of great importance, but only if the architecture—and the company building it—survive long enough for the architecture to be a success. DESIGN CRITERIA FOR INSTRUCTION FORMATS
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Consider an ( n + k) bit instruction with a k- bit opcode and a single n-bit address. This instruction allows 2 ^ k different operations and 2 ^ n addressable memory cells. Alternatively, the same n + k bits could be broken up into a (k − 1) bit opcode, and an (n + 1) bit address, meaning only half as many instructions but either twice as much memory addressable, or the same amount of memory but with twice the resolution. EXPANDING OPCODES
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A ( k + 1) bit opcode and an ( n − 1) bit address gives more operations, but the price is either a smaller number of cells addressable, or poorer resolution and the same amount of memory addressable. Quite sophisticated trade-offs are possible between opcode bits and address bits as well as the simpler ones just described. The scheme discussed in the following paragraphs is called an expanding opcode.
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  • Spring '19
  • Ms. Chit
  • Computer Architecture, Central processing unit, Processor register, Machine code, Pentium 4, ISA level

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