Each line is arranged in three columns called fields
Label field
- May be empty or may specify a symbolic
address consists of up to 3 characters
- Terminated by a comma
Instruction field
- Specifies a machine or a pseudo instruction
- May specify one of
* Memory reference instr. (MRI)
MRI consists of two or three symbols separated by spaces.
ADD OPR (direct address MRI)
ADD PTR I (indirect address MRI)
* Register reference or input-output instr.
Non-MRI does not have an address part
* Pseudo instr. with or without an operand
Symbolic address used in the instruction field must be
defined somewhere as a label
Comment field
- May be empty or may include a comment