Cheats
MAME's cheat system is very powerful and very easy to use. However, it's quite complicated to get running. The cheat system is a LUA plugin which needs to be enabled to run. It can be enabled, on the configuration menu, in the mame.ini file or as the -cheat command line switch. I won't be showing how to make your own cheats as it is very complex however, there is a guide here. Anyway, here's how to do get the cheat system enabled...
The Cheat File
The cheats in MAME are stored as XML files. There are thousands of them, so they are kept in a 7Zip archive called cheat.7z. You can find links to the current cheat files on the Progetto Snaps site here. Once downloaded, all you need to do is drag the archive over to your MAME folder. As for the LUA scripts, these are already in place as they are included in the MAME distribution.
How To Enable The Plugin
There are two ways to enable the cheat plugin. You can open the plugin.ini file in a text editor such as Notepad and change the 0 next to cheat to a 1. You can also enable it in the MAME user interface menus. There is a "Plugins" option on the panel under the games list.
Click it and you'll see this menu...
To enable the cheat system, turn "Cheat plugin" and "Cheat finder help library" to On.
Finally, you need to enable the cheat menu in MAME. As I said above, there are three ways to do this. The first way is to do it from the "Configure Options" menu.
From the settings menu, select "Miscellaneous Options".
You will now see this screen.
Set the cheats option to On and the cheat system is now running. This option will save when you exit MAME.
You can also enable cheats from the command line. Add -cheat to the command line options to enable the cheat system. Here's an example
mame64 -cheat
mame64 <machine> -cheat
Finally you can edit the mame.ini file in a text editor and change the 0 next to cheat to 1. The cheat options is about halfway down the list under # CORE MISC OPTIONS.
Using Cheats
If you have successfully enabled the cheat system then you should see this option appear on the options menu.
Select "Cheat" to open the cheat system's menu.
To enable a cheat, set the one you want to On. Be careful though as enabling too many cheats can crash the machine.