Tandy 1000 MS-DOS Reference Manual page 283

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Chapter 13
THE DEBUG UTILITY
The MS-DOS DEBUG is a utility program to aid you in testing,
changing, and observing the operation of executable object files.
You can use DEBUG to alter the contents of a file or register and
then immediately execute the program to see if the changes are
valid without reassembling the program.
To enter the DEBUG program, type:
DEBUG
[pathname] [parameters]
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ENTER
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• pathname specifies the program file to be loaded into memory.
DEBUG loads the file, starting at lOOR in the lowest available
segment. The BX:CX registers are loaded with the number of
bytes placed into memory.
Omitting the pathname lets you work with the current regis-
ter contents. To load a file into memory, you must use the
Name and Load commands.
Note: When DEBUG is initialized, it sets a program
segment prefix (PSP) at Offset 0 in the program work
area. If you don't specify a pathname, you may over-
write the default PSP. If you are debugging a .com or
.exe file, however, tampering with the PSP below rela-
tive address 5CR will cause DEBUG to terminate.
• parameters is a list of pathname parameters and switches
that are to be passed to the program when it is loaded.
Include parameters only if you included a pathname.
DEBUG displays a hyphen ( - ) to indicate that it is ready to
accept a command.
At initialization, the DEBUG segment registers (CS, DS, DX,
and SS) are set to the bottom of free memory, and the' instruc-
tion pointer (IP) is set to OlOOR. All flags are cleare,d, and the
remaining registers are set to zero.
Do not restart a program after DEBUG displays the message
Program terminated normally.
To reload the program use
the Name and Load commands. Otherwise, it does not run
properly.
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