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OTP (One Time Programmable) is a type of memory of the single-chip microcomputer, which means one-time programmable: after the program is burned into the single-chip microcomputer, it cannot be changed and cleared again.



As embedded applications become more and more widespread, product safety also becomes more and more important. On the one hand, it is to protect the hardware design, on the other hand, it is also for the safety of the product itself, to prevent HACKED.

In an embedded system, all codes and system data are stored in the FLASH chip. The characteristic of FLASH chip is that it can be erased and written many times, and the data will not be lost when power off. In order to protect the data in FLASH, more and more FLASH manufacturers provide a special register in the FLASH: OTP register. OTP=One TimeProgrammable, which means that this register can only be programmed once, and can no longer be modified after programming. The OTP register is very similar to the FLASH data area, 1 can be rewritten to 0, but 0 can never be written as 1. If there is a 32-bit OTP register, the value produced is 0xFFFFFFFF, if the user through programming, write the value of the OTP register After being 0xFFFFFFFE, the OTP register can no longer be rewritten to 0xFFFFFFFF; of course, the value of this OTP register can also be rewritten to 0xFFFFFFFC or other.

In order to provide protection for the OTP register, generally this type of FLASH chip will also provide a LOCK register. The LOCK register (the same OTP) can only be programmed once. Each bit of the LOCK register corresponds to an OTP register. If the bit (BIT) of the LOCK register corresponding to the OTP register is written from 1 to 0, it means that the locked OTP register can no longer be written. Even if the current value of OTP is 0XFFFFFFFF, its value can never be overwritten. Through OTP register and LOCK register, users can save some specific information in OTP, such as software version number, hardware version number, secret key and other information. At the same time, there will be another OTP register in this type of FLASH chip. This register was programmed by the manufacturer when it was produced, written into a specific serial number, and locked. If necessary, FLASH manufacturers can also write a specific serial number according to customer needs. In this way, each chip will have a different ID number to avoid being copied.

In addition to the FLASH chip, many CPU manufacturers also provide similar OTP registers inside the CPU for users to use, which is conducive to the development of safer applications. Like some larger manufacturers, such as TI, FREESCALE, etc., they often do not disclose the data sheets of certain chips. If you want to get their data manual, first, there must be a large number of orders, but also need to sign a certain confidentiality agreement.

OTP itself does not provide absolutely safe applications. However, the provision of OTP is conducive to developers to develop and deploy more secure applications and protect their own interests and customers' interests. Like many large manufacturers, such as NOKIA, MOTOROAL, SAMSUNG and SONYERRICSON, etc., they need to develop some mobile phones that can only be used in their own networks according to the requirements of customers (operators). Many of these software and hardware protections are based on OTP.

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