Motorola HC12 User Manual

User’s Manual

MCUez HC12 Assembler

156

Assembler Syntax

MOTOROLA

All valid user-defined symbols representing memory locations are simple
relocatable expressions. This includes labels specified in XREF directives,
which are assumed to be relocatable symbols.

Expressions involving constants, known as absolute labels, or expressions are
absolute expressions. An expression containing an operation between an
absolute expression and a constant value is also an absolute expression.

Example of absolute expression:

Base:  SET $100

Label: EQU Base * $5 + 3

Expressions involving the difference between two relocatable symbols defined
in the same file and in the same section evaluate to an absolute expression. An
expression as

label2-label1

can be translated as:

(<offset label2> + <start section address >) –

(<offset label1> + <start section address >)

This can be simplified as:

<offset label2> + <start section address > –

<offset label1> - <start section address>

= <offset label2> - <offset label1>

In the following example, the expression

tabEnd-tabBegin

 evaluates to an

absolute expression and is assigned the value of the difference between the
offset of

tabEnd

and

tabBegin

 in the section

DataSec

.

DataSec: SECTION

tabBegin: DS.B  5

tabEnd:   DS.B  1

CodeSec: SECTION

entry:

LDD #tabEnd-tabBegin <- Absolute expression