Radio Shack TRS-80 Model II Reference Manual page 124

MODEL II TRSDOS
This utility 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. You can also use it to make minor replacement changes in
data files.
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.
Note: If you press
during a patch operation, before any changes
have been made in the file,
PATCH
will close the file and return you to
TRSDOS.
The file will be unchanged. Once
PATCH
has begun changing the
file, pressing will have no effect.
Using PATCH on a TRSDOS System File
When Radio Shack releases a modification to
TRSDOS,
you will receive a
printout of the exact
PATCH
commands that are required to perform the
change.
To implement such a change, you would follow these steps:
1. Make a backup copy of the diskette to be patched.
2. Insert the
TRSDOS
disk to be changed into one of the drives. The diskette must be
write-enabled.
3. In the
TRSDOS READY
mode, type in the specified
PATCH
command.
4. After completion of the patch, test the diskette in drive zero to see that it is
operational as a
TRSDOS
system diskette. You will have to reset the Computer.
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