While the global semiconductor industry experienced a downturn, the automotive electronics market performed strongly, particularly with the increasing prevalence of remote control systems. Currently, 60% of cars worldwide are equipped with remote control systems, and according to a Gartner Dataquest report in March 2003, the semiconductor device market consumed by these systems accounted for approximately 5%, amounting to $1.075 billion. The decreasing cost of RF-based remote control components has made electronic remote unlocking systems more cost-effective than mechanical unlocking systems, leading to further market expansion. New applications are also emerging, such as active and passive remote unlocking systems (PKE) and tire pressure monitoring systems, meeting automakers' demands for both safety and ease of use. Active and Passive Remote Unlocking Systems Over the years, active remote unlocking systems have evolved from the initial concept of a transmitter and receiver. The transmitter sends a serial number composed of data to the receiver controller in the car, and the receiver verifies the serial number to determine whether to unlock the door. Early system developers did not consider security issues, failing to anticipate that unauthorized individuals could also receive data via wireless connection. Because most existing systems operate in the 315 or 433 MHz frequency band, car thieves can send various possible serial numbers to unlock doors without damaging them or arousing suspicion. They can also capture the number when the driver opens the door and retransmit it later when no one is around. To mitigate this risk and prevent unauthorized system intrusion, new wireless remote control systems have introduced code-hopping technology, with Keelog being one example. This technology encrypts the incrementing count before sending the code, and the receiver decrypts the code before unlocking the car to ensure the count increments from the previously stored value. As a global standard, Keelog code-hopping technology provides cars with a simple and secure remote control system. Developers can implement a highly secure system with few pins and at a low cost. Furthermore, Keelog is based on a proprietary non-linear encryption algorithm that generates a 32-bit hopping code using a 64-bit programmable cryptographic core. Its programmable nature makes this cryptographic core unique to each device, thus reducing the possibility of unauthorized intrusion. Passive remote unlocking systems are similar to active remote unlocking systems. This system uses two-way wireless communication. It generates a challenge signal from the car to the key, which then encrypts the signal and responds to the car. Therefore, when the driver approaches the car, the key in their pocket is automatically detected. Subsequently, when the driver touches the door handle, if the key is verified, the door unlocks. This method is very attractive to car owners. Tire Pressure Monitoring System In recent years, the public has gained a deeper understanding of tire pressure. Proper tire pressure can save fuel, improve tire life, and enhance vehicle handling. North American legislatures have authorized their Department of Highway Traffic Safety to publish a tire pressure monitoring standard to monitor the internal temperature and real-time pressure of tires in vehicles sold there. With the increasing global consumer demand for safety and fuel efficiency, this standard is expected to be widely recognized and accepted. The core of a tire pressure monitoring system is sensors (pressure and temperature) and a transmitter. When the system is working, the sensors periodically measure the internal pressure, temperature, and battery status of the tire, then transmit the detected data to a receiver via RF, providing the driver with a clear overview of the tire's condition. Typically, each vehicle requires five sensors and transmitters, one for each tire and one for the spare tire. Each transmitter has a unique serial number, allowing the system to distinguish and identify each tire. Furthermore, the sensors and transmitters are placed inside the tire, thus imposing strict requirements on size and weight. Poor control can cause tire imbalance, leading to abnormal tire wear and even safety hazards. It's also worth noting that these sensors and transmitters are battery-powered, requiring batteries with a lifespan of at least 10 years. To assist with power management, tire pressure monitoring system developers use low-frequency communication to activate dormant sensors and transmitters, typically in the 315-433MHz band. These low-power RF designs often use surface acoustic wave (SAW) resonators, enabling low-cost RF transmitters with fewer components. However, due to strict RF emission regulations in Japan and Europe, developers are increasingly turning to phase-locked loops (PLLs) for better frequency stability. In some cases, developers are moving to the 868 or 915MHz bands for better performance, saturation, and reduced low-frequency interference. Remote control system developers must prioritize security. Security issues are often overlooked in applications such as tire pressure monitoring systems (TPMS). A security vulnerability poses a risk of code interception and retransmission attacks. For example, a car thief could identify a target, intercept a pressure detection signal, and then send a low-pressure fault signal. The receiver would then send a fault signal to the driver's display. When the driver reacts and stops, the thief could hijack the vehicle and potentially harm the driver. Two-way communication systems partially address this security risk because the receiver knows when a detection signal should be generated from a specific tire. Furthermore, the limited range of electromagnetic wave communication makes it difficult for thieves to reliably detect and intercept the signal link. Moreover, employing enhanced security techniques such as encryption methods like keelog would further enhance the system's security and reliability, as the timing of tire status queries is randomly generated. Additionally, because TPMS operate in extremely harsh environments, reliable electronic components must be resistant to high temperatures, acceleration, and prolonged use. For instance, antennas placed inside the car can directly affect the reliability of the wireless communication link. Considering ongoing cost pressures, similarities between tire pressure monitoring systems and remote unlocking systems can be leveraged to share certain components. For example, the key's encrypted identification code and the tire pressure measurement signal can both be sent to an RF receiver. The antenna coil used to generate a magnetic field to activate the pressure sensor can also be used to activate the key in a passive remote unlocking system. As remote control systems continue to evolve, new demands will constantly emerge. Therefore, flash-based MCUs will become a key tool for developers to complete hardware and software solutions. Integrating other security systems is also essential while reducing costs and power consumption, as security is a primary factor for consumers when making purchasing decisions.