Chapter 9 Writing Machine Language Instructions and Directive Statements
148 Instruction Statement Fields
9.2.1 Writing Label Field
Labels are called both symbols and names. The assembler assigns a label the value of the location
counter at the point it is defined.
Coding rules
Labels can use upper-case and lower-case letters, digits, underscores (_).
Labels are coded in the first column.
The first character of a label must not be a digit.
Labels are case sensitive.
The same label name cannot be defined twice.
When the label is omitted, it must be replaced with at least one space or tab.
Terminology: * Column
This is a column on the display or printer paper. One character takes one
column. Columns are counted from the left as column 1, 2, etc.
Coding examples
The following examples are incorrect.
LABEL
LONGLABELLONGLABELLONGLABELLONGLAB
main
start_cont
1LABEL ; Starts with a digit
@START ; Uses a prohibited character
START ; Does not start from the first column
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