Application of FRAM in two-way alarm system of automobile
With the popularity of automobiles in China, car theft has become an important issue in car safety. The use of GPS anti-theft, high operating costs, so only for some high-end cars. So how to achieve effective anti-theft of some economical cars, the easiest way is to add a GSM module or CDMA module in the system of simple one-way alarm, you can achieve two-way alarm. This article refers to the address: http:// First clear several concepts: One-way alarm: refers to the alarm sound of the car itself during the alarm period, warning the car thief, reminding the people around the car. This form is the most common, the sensing method is vibration sensing or ultrasonic sensing. (In the spring thunder season , we often hear the car alarm screaming, this way is used by the owner of the car not far from the parking distance alarm. Two-way alarm: When the car sensor (oscillation sensor or ultrasonic sensor) detects an abnormal condition, the car's own alarm is called, warning the thief, and then immediately ruling the owner through an effective way (GSM or CDMA network). Jump code/fixed code door lock: There are two types of car door opening: mechanical lock and remote lock. The remote control lock can be divided into two types: One is fixed, the code is detected every time, the system detects the code, can release the system alarm or start the alarm or open the door or lock the door. The disadvantage is that for high-tech thieves, it can be decrypted by a receiving device. Change the code and then develop the remote control of the same code to open the door or release the alarm. The other is the code hopping, which means that the code transmitted by the remote controller is different each time, so that even if the thief receives the previous remote control code, the remote control that copies the same code cannot open the door. Wireless embedded system: Use the current mature CDMA or GSM network to detect or control the devices and systems in the network through SMS. Since the two-way alarm system currently uses CDMA or GSM networks to notify and control the car, it will increase the wireless operating system with low operating cost. He can save the monthly monthly rent and expensive terminal cost of the GPS, and the driver can know the car. The situation, so it is very popular with consumers. working principle: The car can decode and recognize the remote control code through remote control. When the code is anti-theft code, the sensor of the car starts. When the car is in the anti-theft state, it detects the abnormal condition of the car body, starts the alarm device of the car itself, alarms the thief, and passes the CDMA. Or the GSM module sends a text message or calls the driver to inform the driver. The driver can send a text message to check the car start status, and at the same time, can cut off the car's oil circuit or power supply system, so that the car can not start normally, win the return time, and if the car is at A carjacking on the road, the driver simply presses out the distress signal, can automatically cut off the circuit or oil circuit of the system, and inform his position, so that the reinforcements can arrive at the scene in time. In the system, the main function of EEPROM is memory CDMA control SMS, and the function of storing remote control code. Due to the large and fast data flow of CDMA and the waiting of EEPROM, the system must have a large RAM. In the cache of CDMA data streams, power monitoring can maintain the normal operation of the system. Since the two-way alarm system is basically an improved one-way alarm system, the one-way alarm function is relatively simple, the system adopts the mcu with low configuration, low cost but high reliability, so the mcu RAM will be less, and the CDMA is stored. SMS data must be replaced with a high value mcu, so the cost of RAM space needs to increase the cost of mcu. There is a FRAM solution, which can replace the mcu without the problem of RAM space, and improve the system reliability; FRAM data Storage plan. First understand the characteristics of FRAM: More: more erasing times, 5V power supply FRAM erasing times 100 billion times, low voltage FRAM erasing times is 100 billion times (unlimited times); Fast: fast, the frequency of the CLK of the serial bus FRAM is as high as 20M, and there is no waiting period of 10MS write; the access speed of the parallel port is 70NS; Good: non-volatile (data can be stored for 45 years after power failure, all products are industrial grade, temperature is -40C---85C); working principle: In the system, FRAM is used to control CDMA control SMS; since FM3204 is a multi-function FRAM, its memory read and write is as fast as SRAM, so the data can be directly stored in FM3204, no need to replace the mcu internal RAM. Mcu. At the same time, the FM3204 has a low voltage reset (four-level programming), an independent WDT that can be set up, and a 2.5V comparator to simplify the circuit and improve reliability while reducing cost. FRAM anti-jamming advantage analysis: Since FRAM reads and writes hundreds of millions of times, mcu detects a pulse and can write to FRAM. Because there is no buffer in the ferroelectric memory, the data is written directly to the address corresponding to the FRAM, so the written data will not go wrong, even if the error mcu can be known through the protocol, the anti-interference performance is much better.
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