A Simple Assembly Language
Part of the
Macmillan Computer Science Series
book series (COMPSS)
The simple assembly language (SAL) described here is very similar to the standard manufacturers assembly language for the PDP11 (MACRO11), but certain restrictions have been imposed to enable a simpler smaller assembler to be produced. There is also one addition of some significance, namely the block structure described in Section 5.6 below. All modern programming languages are founded on this notion, and its introduction Into SAL serves to illustrate the principle in addition to being a useful feature. The main characteristics of SAL, which also apply to most other assembly languages are as follows
Each instruction in assembly language corresponds exactly to one machine Instruction.
The function parts of instructions are expressed by their mnemonics. for example. ADD. BNE etc.
Store lines whose addresses are to appear explicitly in instructions are given names.
Values can be associated with names by one of two different mechanisms. First a name can be attached as a label to an instruction and Its value Is then the address of the store line containing the Instruction.