What is the difference between a rolling code remote control and a fixed code remote control?
The so-called fixed code is that the address code issued by the remote control is fixed and unchanged, for example, an encoding chip.
For: 2262 2260 5026-1 5026-2 5026-3 5026-4 FP527 SMC918 PT2240 EV1527 HT12D HT12E and other chip remote control.
Our company usually uses EV1527
Rolling code remote control: The encoder detects the key input and wakes up the system from the power-saving state. The synchronous count plus 1 and the serial number are encrypted with the key to form the cipher text data, and the same key value and other data are sent out. Since the synchronization count value is different every time it is sent, even if the same key is pressed multiple times, it is no exception. Codewords that are automatically scrolled forward while syncing counts no longer occur. Therefore it is called rolling code.
The synchronous count is encrypted by DES together with a 64-bit encoder number. The DES key is unique to the manufacturer and must be kept secret. The encrypted ciphertext is transmitted through the radio frequency system. Since the encryption algorithm can break up the plain text, the rolling code remote control will make the transmitted code change very different and difficult to crack. Due to the existence of synchronous counting, repeated transmission has no effect, so to break this kind of system is to break the DES algorithm. The synchronous count is 16 bits up to 216 = 65536. If it is used 10 times a day, there is a period of 1812 years. A 32-bit serial number with a capacity of 232 = 4.2 billion.
The rolling code encoding method has the following advantages:
(1) Strong confidentiality, the code is automatically changed after each radiation, and others cannot use the "code detector" to obtain the address code.
(2) The coding capacity is large, the number of address codes is greater than 100,000 groups, and the probability of "duplicate code" in use is extremely small;
(3) Easy code matching, the rolling code has the function of learning and storage, no need to use a soldering iron, the code can be matched at the user site, and a receiver can learn up to 10 or dozens of hundreds of different transmitters High flexibility in use;
(4) The error code is small. Due to the advantage of encoding, the receiver's error action when receiving the local code is almost zero.
The fixed code's coding capacity is only 6561, and the probability of heavy code is extremely large. Its code value can be seen through the solder joint connection method, or it can be obtained by using a "code detector" in the field. In the occasions where the confidentiality requirement is low, because of its low price, it is also widely used.
The receiver with a learning key is a rolling code, and the one without a learning key is a fixed code. This is the simplest method of identification.
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