Using KEELOQ to Validate Subsystem Compatibility

Proper modular design can make a system more flexible, easier to maintain and update, and most of all, can help get the design completed faster. In fact, modules or subsystems design can happen in parallel, and can be out-sourced when convenient. Subsystems can also be conveniently replaced during the life of an application to simplify maintenance and allow upgrades. In many situations though, it can be extremely important to verify compatibility of the replacement module in order to ensure the system performs to specifications, maintains quality standards and/or allows safe operation of the whole system. As an example, we offer the case of a mobile phone with its rechargeable battery module. Batteries can be based on different technologies (NiCd, NiMH, Li Ion, etc.) that, in turn, require different charging algorithms. A mismatch would lead to potentially dangerous situations (including as an extreme, fire and explosion of the battery pack) severely compromising the safety of use of the whole product. The situation is different in the case of security applications (such as modular Home Alarm systems) where module validation is required to prevent tampering of the system, theft, and intrusion. This Application Note concentrates on the use of the HCS410 transcoder to implement a reliable (yet low cost) method for module authentication using the KEELOQ technology.