U UNIVAC 1218 - Bitsavers

10 BASIC INFORMATION
SECTION III-A. TRIM I ASSEMBLY SYSTEM
TRIM I is a simple assembly system which converts a source program tape written
with symbolic addressing into an object program tape with absolute addressing
suitable for loading into the computers via the utility packages.
20 SYMBOLIC ADDRESSING
201 LABELS
In an absolute-addressed program every word is assigned an absolute address
during the coding process. In the TRIM I system only those words which are
referred to by instructions require an address, although the address is symbolic
rBther than absolute. The term label is used rather than address since it more
accurately describes the function of the symbolic address. A label may never
be incremented or decremented. Words which are not referred to need not be
labeled o
Unlabeled words following one another on the source program tape are
ultimately assigned to consecutive memory addresses. For any given assembly
run each label used must be unique.
Instructions are written with mnemonic or octal notation for the function and/
or subfunction codes. The u or k portion of an instruction word may be either
a constant, an octal notation,or a symbolic notation (alphanumeric) referring
to a constant (either an absolute address or an item of data).
Whenever any instruction refers to a label, the u portion of that instruction
is called a tag. The tag must be identical with the label to which it refers
but may be followed by a + or - and an octal integer to provide for increments
or decrements. Thus an instruction may refer to an unlabeled instruction in
terms of its sequential position preceding or following a labeled instruction.
Symbolic addressing simplifies the task of coding. In addition it permits the
transfer of programs to any region of memory since the symbolic addressed
program is independent of memory locations.
III-A-l