Introduction To The Rca 70/25 Assembly Language; Format Requirements; Addressing - RCA Spectra 70 Training Manual

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INTRODUCTION TO THE RCA 70/25
ASSEMBLY LANGUAGE
FORMAT REQUIREMENTS
The RCA
70/25
Assembly is an automatic program-
ming system designed to translate a
symbolic
machine-oriented program into a machine-coded
program for subsequent execution on the RCA
70/25
system. The source language consists of one-line
statements written on the RCA Spectra
70
Assembly
Program Form. Each single-line statement per-
forms one of the following functions:
1.
Generates an object program instruction.
2.
Allocates data areas or constants.
3.
Notifies the assembler to perform a specific
function.
OPERATION FIELD
Every statement, except a line used solely for an
output listing comment, must have an entry in the
OPERATION field (Cols.
10-14)
specifying one of
the above three functions.
NAME FIELD
The NAME field (Cols. 1-6 only) may be used when
it is desired to symbolically identify the leftmost
location of the field generated by the statement. The
NAME entry symbol must consist of at least one
alphabetic (A-Z) character followed by any combina-
tion of alphabetic and/or numeric
(0-9)
characters
that do not exceed a total of six characters. The
only exception to the symbol entry above is that an
asterisk may appear in Col.
1 if
the statement line
is to be used for an output listing comment.
OPERAND FIELD
The OPERAND field has entries as required by the
OPERATION field. Thus, if the OPERATION field
specifies that a constant is being defined,
the
OPERAND field entry is the value of the constant.
If an instruction Operation Code appears,
the
OPERAND field must follow the prescribed format
for that particular instruction.
COMMENTS FIELD
A comment may appear in any statement line fol-
lowing the OPERAND entry. It must be separated
from the required OPERAND entry by at least one
blank column. The entire statement line (to Col. 71)
may be used for a comment if an asterisk appears
in Column 1.
14
IDENTIFICATION FIELD
The contents of the IDENTIFICATION field has two
functions. In the START statement, the first four
positions, columns
73-76,
may contain a name to be
assigned to the object program. If the last four
positions, columns,
77-80,
are numeric, the contents
is used as the initial setting ofthe Assembly sequence
counter. If not numeric, the counter starts at all
zeros.
Each object instruction has a sequence
number either derived from the value in columns
77-80
or from zeros.
ADDRESSING
A symbolic name is the most frequently used means
of addressing and referencing a location.
When a
symbol has been used in the NAME field to define a
location,
it
may be referenced as frequently as de-
sired in the OPERAND field. The value assigned is
the address of the left end of the data field or in-
struction on the 'NAMEd' line of assembly coding.
As stated previously, the symbol may be any com-
bination of the alphabetics (A-Z) or numerics
(0-9).
There are two restrictions:
(1)
no name may exceed
six characters,
(2)
the first character must be al-
phabetic.
The following are examples of valid and invalid
symbols:
VALID
Al
STKNKI
C
INI
INVALID
OPN
BEGINERR
IA
IN.I
(Space invalid character)
(Too many characters)
(First character not alphabetic)
(Period invalid character)
The Assembler builds a table containing all the
symbolics that appear in the name field. A specific
HSM address is assigned to each symbolic. The
LOCATION COUNTER, a program counter main-
tained by the Assembler, generates these addresses
and makes assignments. Assume a routine is to
begin at HSM location
2000.

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