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JEDEC Standard No. 251C
Page 5
3.3 Keywords
Several keywords are used to differentiate levels of requirements and options, as follow:
Can - A keyword used for statements of possibility and capability, whether material, physical, or causal
(can equals is able to).
Expected - A keyword used to describe the behavior of the hardware or software in the design models
assumed by this standard. Other hardware and software design models may also be implemented.
Ignored - A keyword that describes bits, bytes, or fields whose values are not checked by the recipient.
Mandatory - A keyword that indicates items required to be implemented as defined by this standard.
May - A keyword that indicates a course of action permissible within the limits of the standard
(may equals is permitted).
Must - The use of the word must is deprecated and shall not be used when stating mandatory
requirements; must is used only to describe unavoidable situations.
Obsolete - A keyword indicating that an item was defined in prior standards but has been removed from
this standard.
Optional - A keyword that describes features which are not required to be implemented by this standard.
However, if any optional feature defined by the standard is implemented, it shall be implemented
as defined by the standard.
Preferred – A keyword used to identify a feature option which is the preferred option to implement for
compliance with anticipated future revisions of this standard.
Reserved - A keyword used to describe objects—bits, bytes, and fields—or the code values assigned to
these objects in cases where either the object or the code value is set aside for future
standardization.
Usage and interpretation may be specified by future extensions to this or other standards. A
reserved object shall be zeroed or, upon development of a future standard, set to a value
specified by such a standard. The recipient of a reserved object shall not check its value. The recipient
of a defined object shall check its value and reject reserved code values.
Shall - A keyword that indicates a mandatory requirement strictly to be followed in order to conform to
the standard and from which no deviation is permitted (“shall” equals “is required to”). Designers are
required to implement all such mandatory requirements to assure interoperability with other products
conforming to this standard.
Should - A keyword used to indicate that among several possibilities one is recommended as particularly
suitable, without mentioning or excluding others; or that a certain course of action is preferred but not
necessarily required; or that (in the negative form) a certain course of action is deprecated but
not prohibited (“should” equals “is recommended that”).
Will - The use of the word will is deprecated and shall not be used when stating mandatory requirements;
will is only used in statements of fact.
3.4 Abbreviations
etc.: And so forth (Latin: et cetera)
e.g.: For example (Latin: exempli gratia)
i.e.: That is (Latin: id est)
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JEDEC