Master codes are used to acces a page on your STB MENU, where you can edit keys to open scrambled channels. The master code is used together with a procedure, and they both differ from receiver to receiver.
let me tell you that master code are ONLY ussefull when you forgot the parental code(pincode)
normaly when you buy a receiver the defuallt code = 0000
but you can change this any time and when you forgot this new pincode you can use the mastercode to get acces again to any pages in the menu
and it has nothing to do with scrambeld channels