2.8
Machine Language Program Control
Statements
Several machine language program
control
statements are suported
by
the
MZ-700 BASIC interpreter.
With these statements, machine language programs can be linked with a
BASIC program.
Computer
programming languages form a hierarchical structure
as
shown below. High level languages such
as
BASIC automatically performs work required when lower level languages such
as
assembly language are
used. Although high level languages are convenient and easy
to
use, they cannot control the CPU directly.
The lowest level language (machine language) directly controls the
CPU and provides high processing
speed,
but
considerable skill
is
required for coding long programs.
Machine language program control statements enable sophisticated programming techiques which make it
possible
to
utilize the advantages
of
both
BASIC and machine language.
Machine language programs can be generated and loaded
into
the machine language program area (reserved
with
the
BASIC LIMIT statement) using
the
monitor
or assembler and loader. Such machine language
programs can be called
by
BASIC programs
with
-
the
USR ( ) function. Machine language programs
can also be loaded into
memory
using a BASIC program which uses the POKE statement
to
write each
step in machine code.
the
resultant machine language program can then be called
by
BASIC programs
with
the
USR ( ) function.
The memory map
at
bottom
right outlines the concept
of
data access with POKE and PEEK, and
of
calling machine language programs with USR (
).
$0000
r---------------------,
US R
C$
8
000)
SYS
TEM
BASIC program
POKE PEEK
LIMIT
~b-...--r....,..-,-+-....,......,-,-T--7---r-?"--r-7-r-;"""'7K
$ A F F F
Machine language
program
area
All
RAM
in the
700
mode
----------------------------------------
------------------
--~--
--------91
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