Reference Guide

Chapter 2 21

Program Structure

Symbols and Constants

Both addresses and constants can be represented symbolically. Labels

represent a symbolic address except when the label is on an .EQU, .REG,

or .MACRO directive. If the label is on an .EQU or .REG directive, the

label represents a symbolic constant. If the label is the .MACRO directive,

the label represents a macro name.

Symbols are composed of uppercase and lowercase letters (A-Z and a-z),

decimal digits (0-9), dollar signs ($), periods (.), ampersands (&), pound

signs (#), and underscores (_). A symbol can begin with a letter, digit,

underscore, or dollar sign. If a symbol begins with a digit it must contain

a non-digit character. (The predeﬁned register symbols begin with a

percent sign (%).)

The Assembler considers uppercase and lowercase letters in symbols to

be distinct. The mnemonics for operation codes, directives, and

pseudo-operations can be written in either case. There is no explicit limit

on the length of a symbol. The following are examples of legal symbols:

$START$ _start PROGRAM M$3 $global$

$$mulI main P_WRITE loop1 1st_time

The following are examples of illegal symbols:

LOOP|1 Contains an illegal character

&st_time Begins with &

123 Does not contain a nondigit

Integer constants can be written in decimal, octal, or hexadecimal

notation, as in the C language. “Integer Constants” on page 22 lists the

ranges of these integer constants.