From-Machine-Language-to-Assembly-Language

• Each line of a program is one of the following:
  • an instruction
  • an assembler directive (or pseudo-op)
  • a comment
• Whitespace (between symbols) and case are ignored.
• Comments (beginning with “;”) are also ign

LABEL OPCODE OPERANDS COMMENTS

• optional: Label, Comments
• mandatory: Opcode, Operands

• Opcodes:
  • reserved symbols that correspond to LC-3 instructions
  • example: ADD, AND, LD, LDR
• Operands：
  • Registers:
  • Numbers: #(DEC) or x(HEX)
  • Label: symbolic name oof memory location

placed at the beginning of the line
assigns a symbolic name to the address corresponding to line

Loop ADD R1,R1,#-1
     Brp LOOP
Copy

• Anything after a semincolon is comments
• Ignored by assembler
• Used by humans to document/ understand programs
• Tips for useful comments:
  • avoid restating the obvious, as “decrement R1”
  • provide additional insight, as in “accumulate product in R6”
  • use comments to separate pieces of program

Pseudo-operations

• Do not refer to operations executed by program
• used by assembler
• look like instruction, but "opcode" starts whith dots