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4.7
ASSEMBLY/DISASSEMBLY PROCEDURES
The assembler/disassembler is an interactive assembler/editor. Each source line is converted into
the proper machine language code and is stored in memory overwriting previous data on a line-
by-line basis at the time of entry. In order to display an instruction, the machine code is
disassembled and the instruction mnemonic and operands are displayed. All valid opcodes are
converted to assembly language mnemonics. All invalid opcodes are displayed on the terminal
CRT as "ILLOP".
The syntax rules for the assembler are as follows:
• All numerical values are assumed to be hexadecimal. Therefore no base designators
(e.g., $ = hex, % = binary, etc.) are allowed.
• Operands must be separated by one or more space or tab characters.
• Any characters after a valid mnemonic and associated operands are assumed to be
comments and are ignored.
Addressing modes are designated as follows:
• Immediate addressing is designated by preceding the address with a # sign.
• Indexed addressing is designated by a comma. The comma must be preceded a one
byte relative offset (even if the offset is 00), and the comma must be followed by an X
or Y designating which index register to use (e.g., LDAA 0,X).
• Direct and extended addressing is specified by the length of the address operand (1 or
2 digits specifies direct, 3 or 4 digits specifies extended). Extended addressing can be
forced by padding the address operand with leading zeros.
• Relative offsets for branch instructions are computed by the assembler. Therefore the
valid operand for any branch instruction is the branch-if-true address, not the relative
offset.
M68HC11EVBU/D
OPERATING INSTRUCTIONS
4-35
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