Chapter
1.
Assembly
language
and
Processors
Symbol-Cross-Reference Listing
The symbol-cross-reference listing
is
another
of
the diagnostic tools provided
by
the assembler. Assume, for
example,
that
your program manipulates a data field named DATE, and
that
testing reveals a program logic
error
in
the handling
of
this data. The symbol-cross-reference listing simplifies debugging this error because
it
points you to each instruction
that
references the symbol DATE.
Do You Need
the
Assembler?
The assembler
is
but
one
of
several tools available for developing microprocessor programs. Typically, choosing
the most suitable tool
is
based on cost restraints versus the required level
of
performance. You or your company
must determine cost restraints; the required level
of
performance
depend,
on a number
of
variables:
•
The number
of
programs to
be
wl'itten: The greater the number
of
programs to
be
written, the more
you need development
support.
A.lso,
it
must
be
pointed
out
that
there can
be
penalties for not
writing programs. When your application has access to the power
of
a microprocessor, you may
be
able to provide customers with custom featur'es through program changes. Also, you may
be
able to
add features through
programmin:~.
• The time allowed for progr'amming:
As
the time allowed for programming decreases, the need for
programming
support
increases.
• The level
of
support
for existing programs: Sometimes programming errors are not discovered until
the program has been
in
use
for quite a while. Your need for programming
support
increases
if
you
agree to correct such errors for your
customers. The number
of
supported programs
in
use can
mUltiply this requirement. Also, program
support
is
frequently subject to stringent time constraints.
If
none
of
the factors described above apply to your' situation, you may
be
able to get along without the
assembler.
Intel", PROMPT-80, for example, ,lllows you to enter' programs directly into programmable read only
memory.
You enter the program manually as a string
of
hexJdecimal digits. Such mJnual programming
is
relatively
slow and more prone to human error than computer-assisted programming.
However, manual systems are
one
of
the least expensive tools available for
micropmce,sor
programming. Manual
sy<;1ems
may
be
suitable for limited
applications, hobbyists, and those who want to explore possible applications for microprocessors.
If
most
of
the factors listed previously apply to
you,
you should explore the advantages
of
PL(M. PL(M
is
Intel's high-level language for program development. A high-level language
is
directed more to problem solving
than to a particular" microprocessor. This
allows you to write programs much more quickly than a hardware-
oriented language such
as
assembly language.
As
an example, assume
that
a program must move five characters
from
one
location
in
memory to another". The following example illustrates the coding differences between
assembly language and
PL(M. Since instructions have not
yet
been de,cribed, the a,sembly language instructions
are represented by a flowchart.
1-3
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