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microcode    音标拼音: [m'ɑɪkrok,od]
微码

微码

microcode
微码;微程式码

microcode
微码

microcode
n 1: (computer science) coded instructions that are stored
permanently in read-only memory [synonym: {firmware},
{microcode}]

A technique for implementing the {instruction
set} of a processor as a sequence of microcode instructions
("microinstructions"), each of which typically consists of a
(large) number of bit fields and the address of the next
microinstruction to execute. Each bit field controls some
specific part of the processor's operation, such as a gate
which allows some {functional unit} to drive a value onto the
{bus} or the operation to be performed by the {ALU}. Several
microinstructions will usually be required to fetch, decode
and execute each {machine code} instruction
("{macroinstruction}"). The microcode may also be responsible
for {polling} for hardware {interrupts} between each
macroinstruction. Writing microcode is known as
"microprogramming".

Microcode may be classified as "horizontally encoded" or
"vertically encoded". Horizontal microcode is as described
above where there is a fairly direct correspondence between
the bit fields in a microinstruction and the control signals
sent to the various parts of the CPU. Not all combinations of
bits will be valid (e.g. two units driving the bus at once).
Vertical microcode is closer to {machine code} because a bit
field value may pass through some intermediate combinatory
logic which generates the actual control signals. This allows
a few bits of a microinstruction to determine several control
signals and ensure that only valid combinations of those
signals are generated (e.g. a field may be decoded to determine
which unit drives the bus). The disadvantage with vertical
encoding is that the encoding is usually fixed and takes extra
time compared with horizontal encoding which allows any
combination of signals to be generated and takes no time to
decode.

The alternative to a microcoded processor is a {hard-wired}
one where the control signals are generated directly from the
bits of the {machine code} instruction. This is more common
in modern {RISC} architectures because it is faster.

Microcode is usually stored in {ROM} chips though some
processors (e.g. the {Orion}) use fast RAM, making them
dynamically microprogrammable.

(1996-11-26)


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英文字典中文字典相关资料:


  • 1 - Wikipedia
    1 (one, unit, unity) is a number, numeral, and grapheme It is the first and smallest positive integer of the infinite sequence of natural numbers
  • 1 - Wiktionary, the free dictionary
    Tenth century “West Arabic” variation of the Nepali form of Hindu-Arabic numerals (compare Devanagari script १ (1, “éka”)), possibly influenced by Roman numeral Ⅰ, both ultimately from using a single stroke to represent the number one
  • 1 (number) - New World Encyclopedia
    The glyph used today in the Western world to represent the number 1, a vertical line, often with a serif at the top and sometimes a short horizontal line at the bottom, traces its roots back to the Indians, who wrote 1 as a horizontal line, as is still the case in Chinese script
  • The number one - Britannica
    The number 1 symbolized unity and the origin of all things, since all other numbers can be created from 1 by adding enough copies of it For example, 7 = 1 + 1 + 1 + 1 + 1 + 1 + 1
  • Number 1 - Curious Math Facts and Interesting Properties
    In a nutshell 1 is an odd number which is uniquely neither prime nor composite It is known as the multiplicative identity or unit It’s also the only positive number with no other divisors
  • About The Number 1 - numeraly. com
    The number 1 is unique in many ways, and holds a fascinating position in the world of mathematics, science, and culture As the first whole number, it is the foundation for all other numbers and serves as the starting point for counting
  • 1 Definition Meaning - Merriam-Webster
    one 1 of 3 adjective ˈwən ˌwən 1 : being a single unit or thing see number 2 : being a certain unit or thing
  • What Is 1? Definition, Facts Examples for Kids - Vedantu
    Discover what the number 1 means with fun examples Learn how to write 1 in words and boost your maths skills with Vedantu!
  • What does 1 mean? - Definitions. net
    1 (one, also called unit, unity, and (multiplicative) identity) is a number, and a numerical digit used to represent that number in numerals It represents a single entity, the unit of counting or measurement
  • 1 -- from Wolfram MathWorld
    Although the number 1 used to be considered a prime number, it requires special treatment in so many definitions and applications involving primes greater than or equal to 2 that it is usually placed into a class of its own (Wells 1986, p 31)





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