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Opcode abbreviated from operation code is the portion of a machine language instruction that specifies the operation to be performed. Base instructions form a Turing-complete instruction set. Object model instructions provide an implementation for the Common Type System.
Opcode for OR 0,0,0. [7] LDI 26,0: 4 0x34000034 Palindromic NOP - that is, an instruction that executes as NOP regardless of whether byte order is interpreted as little-endian or big-endian. Some PA-RISC system instructions are required to be followed by seven palindromic NOPs. [7] POWER, PowerPC, Power ISA: NOP: 4 0x60000000 Opcode for ori r0 ...
The Intel 8085 ("eighty-eighty-five") is an 8-bit microprocessor produced by Intel and introduced in March 1976. [2] It is the last 8-bit microprocessor developed by Intel. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added interrupt and serial input/output features.
New opcodes that introduced new functionality (e.g. SHLD, SETcc) For instruction forms where the operand size can be inferred from the instruction's arguments (e.g. ADD EAX,EBX can be inferred to have a 32-bit OperandSize due to its use of EAX as an argument), new instruction mnemonics are not needed and not provided.
For example, the x86 architecture has available the 0x90 opcode; it is represented as NOP in the assembly source code. While it is possible to write programs directly in machine code, managing individual bits and calculating numerical addresses is tedious and error-prone.
In 1979, even after the introduction of the Z80 and 8085 processors, five manufacturers of the 8080 were selling an estimated 500,000 units per month at a price around $3 to $4 each. [ 23 ] The first single-board microcomputers , such as MYCRO-1 and the dyna-micro / MMD-1 (see: Single-board computer ) were based on the Intel 8080.
A sample program is provided below to get an idea of what a SIC program might look like. In the code below, there are three columns. The first column represents a forwarded symbol that will store its location in memory. The second column denotes either a SIC instruction (opcode) or a constant value (BYTE or WORD).
Some instruction sets have nearly uniform fields for opcode and operand specifiers, whereas others (e.g., x86 architecture) have a less uniform, variable-length structure. [10] [11] Instruction sets can be extended through the use of opcode prefixes which add a subset of new instructions made up of existing opcodes following reserved byte ...