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PCB Reverse Engineering

AVR microcontroller IC decryption after writing chip considerations

 AVR microcontroller IC decryption after writing chip considerations
AVR microcontrollers IC decryption have multiple sets of fuse locations related to the device configuration and operating environment. These fuses are very important. Users can set and configure the Fuse to make the AVR microcontroller different in nature to suit the practical application. But because of the need to configure the fuse, to the beginners to bring some not very understanding of the place, after decryption of the microcontroller, the program in the burning time, but also on the fuse configuration, if the configuration is wrong, may not Work or function changes. All in the burning of decrypted documents when the fuse must be configured, because the tools to support AVR is very much, and different tools of the software interface is different, so do the best in the AVR microcontroller decryption before deciphering the company itself What tools are used, so that the chip decryption company in accordance with their own tools to do the interface map, so easy to decrypt after the program to burn, but they can also use the decryption company to provide samples to read the fuse configuration, and some Tools can read the chip directly, some read configuration, etc., and then read out the configuration saved.
If it is just the factory single-chip, the default is to use the internal 1MHZ RC oscillation as the system clock, and JTAG port is in the allowable mode. For the AVR fuse at least to clear the following points.
1, AVR fuse can be programmed several times, not a one-time OTP fuse.
2, the fuse bit configuration can be achieved in parallel, ISP and JTAG serial mode.
3, AVR chip encryption lock (LB2 / LB1 = 1 / 0,0 / 0) can not read the chip through any FLASH and EEPROM data, but the status of the fuse can still be read, but can not modify Configuration.
4, the chip erase command is to FLASH and EEPROM data clear, and at the same time the two-bit lock bit status is configured to no lock state (LB2 / LB1 = 1/1), but the chip erase command does not change the other fuse Bit state.
5, download the correct steps are: in the chip without locking the chip to download the running code and data, configure the relevant fuse bit, and finally configure the chip encryption location.
6, the chip is encrypted and locked, if found fuses and configuration is wrong, you must use the chip erase command to clear the data in the chip, decrypt the encryption lock, and then re-download the running code and data, modify the configuration-related fuses , And finally re-configure the chip's encryption lock bit.
7, need to be very clear that the SPIEN bit, a lot of customers have been telephone consultation, that is, we provide the microcontroller can not be connected with the ISP, and can buy their own, the fuse for the SPIEN is configured ISP, if SPIEN is 1, ISP is allowed state, if it is 0 to prohibit the state, if it is prohibited state of course, can not ISP port chip.
8, and more important is the BOOTRST bit, this bit set the relationship between the chip after power-on program from 0X0000 or from the BOOT area began to implement. The choice of the system clock source is also very important, after decrypting the program when the client is often not easy to use, playing part of the clock source is not set because of the reasons, so the system clock must be in accordance with the original settings.
As a result of the use of different tools, IC decryption programming methods and requirements of the documents are also different.
One way is to use a common programmer method, if the use of general programmers, generally support BIN or HEX file, directly load the file, and then the corresponding configuration, you can directly burn.
Second, another method is to use ISP or JTAG download line mode to write the file, because there are many kinds of download lines, the general download line are supported in the AVRSTUDIO download, STUDIO download, the required file format must be HEX Formatted files, if loaded BIN file, will be prompted not AVRSTUDIO support format. And require FLASH and EEPROM files are downloaded separately, that is, after the decryption to provide FLASH and EEPOM two files.



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