Table of Contents
Advertisement
62
Assembly Language Fundamentals
The primary purpose of this capability is to allow as much modularity in the listings as you can
get in source code. To implement this purpose, a "listing counter" is used.
Whenever an LST instruction is encountered during an assembly, the listing counter is in-
cremented. Whenever an UNL instruction is encountered during an assembly, the listing
counter is decremented. Source lines are listed whenever the counter is greater than O.
Whenever it is equal to 0 or negative, then no lines are listed.
The counter is set to 0 upon execution of the !ASSEMBLE statement. This is why there is no
automatic listing. However, if the LIST option is included in the IASSEMBLE statement, then
the counter is initialized to 1. This is why that option creates a listing. Thus, you could defeat a
LIST option by placing an UNL instruction at the beginning of a module. This initialization
occurs for each module assembled, so if you have more than one module indicated in your
IASSEMBLE statement, the counter is set at the beginning of the assembly for each.
This capability sees its greatest usefulness during debugging stages and while working with
independently written sections of source code. For example, a number of people could be
writing different sections of code, each containing their own LST and UNL instructions. These
instructions could then be overridden when they were combined into a single module by
preceding the sections with an LST instruction (to get a listing) or an UNL (to suppress the
listings).
Page Format
Each and every assembly listing page has the following format-
• The word "PAGE" and the current page number of the listing occurs on the first line
starting at column 49 .
• A heading occurs on the second line, left-justified. The heading always includes -
where {name} is the name of the module currently being assembled. Additional heading
information can be specified for this line (see "Page Heading" below).
Advertisement
Table of Contents
