Assembly/Disassembly Procedures - Motorola M68HC11EVB User Manual

OPERATING INSTRUCTIONS

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: (a.) All numerical values are assumed to be
hexadecimal. Therefore no base designators (e.g., $ = hex, % = binary, etc.) are allowed. (b.)
Operands must be separated by one or more space or tab characters. (c.) Any characters after a
valid mnemonic and associated operands are assumed to be comments and are ignored.
Addressing modes are designated as follows:
preceding the address with a # sign. (b.) 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 00,X). (c.) 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. (d.) 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.
Assembler/disassembler subcommands are as follows. If the assembler directs an error in the new
source line, the assembler will output an error message and then reopen the same address
location.
/
^
<CR>
(CTRL)J
(CTRL)A
4-34
Assemble the current line and then disassemble the same address location.
Assemble the current line and then disassemble the previous sequential
address location.
Assemble the current line and then disassemble the next opcode address.
Assemble the current line. If there isn't a new line to assemble, then
disassemble the next sequential address location. Otherwise, disassemble
the next opcode address.
Exit the assembler mode of operation.
(a.) Immediate addressing is designated by
M68HC11EVB/D