Radio Shack TRS-80 Model III - Technical Information; To Protect High RAM

OPERATION
12/Technical
Information
This
section is
intended
for Z-80
programmers
and
BASIC
programmers who
are
familiar
with binary
and
hexadecimal
arithmetic
and
hardware
concepts
like bit
and
byte.
Its
purpose is to
allow you to
take
full
advantage
of the
Model HI
TRS-80.
If
you
want
to
understand
and use
the
system
on this
level
,
but
do not
have the
background,
we
suggest you
read:
TRS-80
Assembly
Language
Programming
by
William
Barden,
Jr.
Radio
Shack
Catalog
Number
62-2006
This one
book
will get you
off to
a good
start. It
was
written
for the
Model I
TRS-80,
but almost
all of
it applies to
the
Model HI
as
well
.
To
Protect
High
RAM
In
many
applications, you
will want to
interface
a BASIC
program
and a Z-80
routine.
In such
cases, you
need
to
protect
enough
high
RAM to
accommodate
your
Z-80
routine.
Otherwise,
BASIC
will
use
all RAM
available for
storage and
execution
of the BASIC
program.
During
the
start-up
dialog, you
have the
option
of protecting
high
RAM via
the
Memory Size
Question.
If you
simply
press
(ENTER) to
this
question,
BASIC
will use
all
available
RAM.
To
protect
RAM,
type in
the
'
'limit
address"
in
decimal
form,
and then
press
(ENTER) . The
limit
address
is the
highest
memory
address you
want BASIC to
use.
Addresses
above this
value
will
not be
affected by
BASIC.
For
example, if you
type:
"32667
(ENTER)
",
BASIC
will not
use
any memory
above
32667. It will
use
32667
and all
lower-numbered
memory
locations.
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