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Ax51 User's Guide
Ax51 Introduction Assembling Programs 
Writing Assembly Programs Assembly Statements 
Controls Instructions Comments Symbols and Symbol Names Labels Using Operands and Expressions Special Assembler Symbols Immediate Data Memory Access DATA BIT IDATA EDATA XDATA CODE Program Addresses Expressions and Operators Numbers Characters Character Strings Location Counter Operators ( ) * + - / < <= <> == > >= AND BYTEx EQ GT GTE HIGH LOW LT LTE MBYTE MOD NE NOT OR SHL SHR WORDx XOR Class Operators Expressions Expression Classes Relocatable Expressions Simple Relocatable Expressions Extended Relocatable Expressions Expressions Example Control Statements Macro Processor Error Messages AppendixUsing Operands and Expressions
Operands are arguments, or expressions, that are specified along with assembler directives or instructions. Assembler directives require operands that are constants or symbols. For example:
VVV EQU 3
DS 10h
Assembler instructions support a wider variety of operands than do directives. Some instructions require no operands and some may require up to 3 operands. Multiple operands are separated by commas. For example:
MOV R2, #0
The number of operands that are required and their types depend on the instruction or directive that is specified. In the following table, the first four operands can also be expressions. Instruction operands can be classified as one the following types:
| Operand Type | Description |
|---|---|
| Immediate Data | Symbols or constants the are used as an numeric value. |
| Direct Bit Address | Symbols or constants that reference a bit address. |
| Program Addresses | Symbols or constants that reference a code address. |
| Direct Data Addresses | Symbols or constants that reference a data address. |
| Indirect Addresses | Indirect reference to a memory location, optionally with offset. |
| Special Assembler Symbol | Register names. |
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