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Minimal instruction set computer (MISC) is a central processing unit (CPU) architecture, usually in the form of a microprocessor, with a very small number of basic operations and corresponding opcodes, together forming an instruction set. Such sets are commonly stack-based rather than register-based to reduce the size of operand specifiers.
Hardwired into a CPU's circuitry is a set of basic operations it can perform, called an instruction set. Such operations may involve, for example, adding or subtracting two numbers, comparing two numbers, or jumping to a different part of a program. Each instruction is represented by a unique combination of bits, known as the machine language ...
The types of operations may include arithmetic, data copying, logical operations, and program control, as well as special instructions (e.g., CPUID). [10] In addition to the opcode, many instructions also specify the data (known as operands) the operation will act upon, although some instructions may have implicit operands or none at all. [10]
The MIPS architecture provides a specific example for a machine code whose instructions are always 32 bits long. [5]: 299 The general type of instruction is given by the op (operation) field, the highest 6 bits. J-type (jump) and I-type (immediate) instructions are fully specified by op.
A microprocessor is a computer processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, and control circuitry required to perform the functions of a computer's central processing unit (CPU).
(In the examples that follow, a, b, and c are (direct or calculated) addresses referring to memory cells, while reg1 and so on refer to machine registers.) C = A+B 0-operand (zero-address machines), so called stack machines: All arithmetic operations take place using the top one or two positions on the stack: [9] push a, push b, add, pop c.
PMIO was very useful for early microprocessors with small address spaces, since the valuable resource was not consumed by the I/O devices. The best known example of a PC device that uses programmed I/O is the Parallel AT Attachment (PATA) interface; however, the AT Attachment interface can also be operated in any of several DMA modes.
The MOS Technology 6502 is an example of a microprocessor using a PLA for instruction decode and sequencing. The PLA is visible in photomicrographs of the chip, [12] and its operation can be seen in the transistor-level simulation. Microprogramming is still used in modern CPU designs.