Identifiers

Identifiers are names that identify the following items:

devices

device pins or nodes

functional blocks

sets

input or output signals

constants

macros

dummy arguments

All of these items are discussed later in this chapter. The rules and restrictions for identifiers are the same regardless of what the identifier describes.

The rules governing identifiers are listed below:

Identifiers can be up to 31 characters. Longer names are flagged as an error.

Identifiers must begin with an alphabetic character or with an underscore.

Other than the first character, identifiers can contain upper- and lowercase characters, digits, tildes (~), and underscores.

You cannot use spaces in an identifier. Use underscores or uppercase letters to separate words.

Except for Reserved Identifiers (Keywords), identifiers are case sensitive: uppercase letters and lowercase letters are not the same.

You cannot use periods in an identifier, except with a supported dot extension.

Some supported identifiers are listed below:

HELLO
hello
K5input
P_h
This_is_a_long_identifier
AnotherLongIdentifier

Some unsupported identifiers are listed below:

7_ Does not begin with a letter or underscore
$4 Does not begin with a letter or underscore
HEL.LO Contains a period (.LO is not a valid dot extension)
b6 kj Contains a space

The last of these identifiers is interpreted as two identifiers, b6 and kj.

Reserved Identifiers (Keywords)

Choosing Identifiers