How To Find Cheats For Machine Code Games
By M.T.Farnworth (16C)
Finding a cheat for a game is something that most people wish they could
do. There never seems to be a cheat available for the game you are having
the most trouble with.
There are two methods of finding cheats:
a) Studying the program and then altering the necessary instruction.
b) Trial and error.
The first of the two alternatives can take a long time especially if you
are not used to comprehending machine code.
The second also sounds like a long drawn out process, as changing every
part of the program, and then testing it could take months.
However you do not need to change every instruction in the program, only
the ones that could have some reference to what you are trying to do.
For example most of the time people are interested in having infinite
lives. The programmer will normally store the number of lives in a memory
location in zero page, so the quickest way of reducing the number of lives
There are not normally very many DEC instructions in a program, and very
few indeed referring to zero page locations, so it does not take long to
change them all individually and play the game.
I think that I should point out that when I say change the instruction I
mean replace it with NOP (No OPeration). This will prevent the number of
lives being reduced.
Finding and replacing the instruction could not be simpler. Just load up
an unchanged version of the program. Then using a simple BASIC program
find the value &C6 (represents DEC &xx) in the program and change it for
&EA (NOP) along with the byte after it which would have been the second
half of the the instruction.
An example program is:
10 *LOAD original 2000
40 FOR I%=1 TO occurrence
70 UNTIL ?counter=&C6 OR counter>lengthoffile+start
90 IF counter>lengthoffile+start PRINT"Not found":END
110 OSCLI"SAVE hacked 2000+"+STR$~lengthoffile+" "+STR$~executeaddress+"
The load address, execute address, and length of file will vary from
program to program so you will have to change them according to which file
you are altering. Their values for each particular game can be found by
The program listed will change the first zero-page DEC command, and the
address byte after it, into two NOPs. After running this program the first
time you would then test the game. If it did not achieve the results you
wanted (more than likely), you would then start again, but set occurrence
at 2, so that it will change the second zero-page DEC instruction it comes
across, and so on.
When using a program such as the one above it is best to copy all the
files connected with the game onto a blank disk then rename the file which
you which to place the cheat into. When the program has run it should
save the file under the original name. Then it is a simple matter of
loading the game as usual but the altered file will be loaded instead.
This method will save you messing around with the filenames in programs.
e.g. If the file is called POWER it could be renamed POWERX. Then when
POWERX is modified it would be saved as POWER.
It should be remembered at this time that DEC can also be used in many
other ways, each of which produce a different OPCODE.
e.g. DEC &xxxx has opcode &CE
When looking for this instruction line 100 of the above program would be
Table of useful Opcodes
Mnemonic Opcode No of Bytes
======== ====== ===========
DEC &xx &C6 2
DEC &xxxx &CE 3
SBC #xx &E9 2
STA &xx &85 2
STA &xxxx &8D 3
The opcodes above are a good start when attempting to write an infinite
lives cheat. STA is useful as it prevents new values being stored in
memory. So if they are not using DEC it is highly likely that preventing
an STA will maintain lives at their set level. However STA is one of the
most commonly used commands so there will be many occurrences of it in the
program; you will have a lot of errors in your trial & error!
Please remember that the list above is not a definitive guide and other
instructions may have been used. In games where damage is recorded
commands such as INC and ADC should be checked instead.
You now have enough information to write a cheat for most games, so I will
leave you to do your cheat writing.
Remember finding cheats is fun, and you can often end up with some
If you wish to contact me directly please write to:
27 Hunt St
Or else write to me via the 8BS messaging system (which is a lot slower!)