资料介绍
Remote Control Systems
Remote control via RF or IR is popular for many appli-cations, including vehicle alarms and automatic garage
doors. Conventional remote control systems are based
on unidirectional transmission and have limited secu-rity. More sophisticated devices based on bidirectional
transmission are also available but, because of their
high cost and certain practical disadvantages, they are
not widely used in commercial remote control devices.
The popular unidirectional transmission systems cur-rently have two very important security shortcomings:
the codes they transmit are usually fixed and the num-ber of possible code combinations is relatively small.
Either of these shortcomings can lead to unauthorized
access. TB003
An Introduction to KEELOQ Code Hopping
Author: Kobus Marneweck A remote control transmitter of the type normally used
Microchip Technology Inc. in vehicle security systems, is nothing but a small radio
transmitter that transmits a code number on a certain
frequency. This code number is normally generated by
INTRODUCTION an integrated circuit encoder. The transmit frequency is
norma