Radio Shack TRS-80 Owner's Manual page 72

RS-80
MODEL
111
DISK
SYSTEM
This
command
lets
you make
minor
corrections
in
any
disk
file,
provided
that:
1.
You
know
the existing contents
and
location of
the data
you want
to
change.
2.
You want
to
replace
one
string
of
code
or data with another
string
of the
same
length.
You
can use
patch
to
make
minor changes
to
your
own
machine-language
programs;
you won't have
to
change
the
source code, re-assemble
it,
and
re-
create the
file.
Another
application for
patch
is
to
allow you
to
implement any
modifications
to
trsdos
that
may
be supplied
by Radio Shack. That way, you do
not
have
to
wait
for a
later
release
of
the
operating system.
Sample Use
Suppose you want
to
change seven
bytes
in a
machine-language program
file.
First
determine
where
the seven-byte sequence
resides
in
ram
when
the
program
is
loaded.
Then make
sure your replacement
string
is
the
same
length
as
that
of the original
string.
For example, you might
write
down
the
information
as follows:
File to
be changed:
vread
Start
address:
x'5280'
Sequence
of
code
to
be changed:
x'CD2D25E5'
Replacement
code:
x*ooooooo9*
Then you
could use
the
following
command:
PATCH UREAD
(
ADD=5280 *FIND=0CD2D25E5 »CHG=00000009
PAUSE
Pause Execution
for
Operator
Action
pause
message
message
is
;ha :r<ssi3$?
lo
'??.
>i\viv?.\^-.
tii':^
^t
i&i^'
:
-
.^scs^-f:.
'.^
56