Read MCU need to be executed in different ways and one of the most secure one is read the MCU from an already removed memorizer. Unfortunately this MCU read technology can only be applied on quite few of EEPROM/Flash chip.

First, some MCU memorizers such as MSP430 series from TEXAS INSTRUMENT, has the embedded voltage stabilizer circuit to tamper read. raise the power supply voltage from 1.8V to 3.6V won’t affect the read operation from partial erasable unit when read MCU. Lots of microcontroller will reset completely and release the control circuit in the memorizer when MCU reset or reenter the programmable mode. However, if the content of memorizer didn’t vanish completely after MCU read, it will cause a severe problem, that is all the security systems are all assume that flash content can’t be regained after a memorizer erase cycle after MCU read. if the un-invasive read is not working, then the invasive MCU read could be workable. For example, the control circuit in the MCU can be modified by Focus Ion Beam, or alter the reference voltage directly, current source or control grid voltage.

Finally, some MCUs need to be erased before the programming of its memorizer and read. which makes it impossible to read MCU and acquire any information from already erased memorizer. Some microcontroller protection fuses don’t have a correct design, and fuse will be erased earlier than memorizer. If the MCU read and erase operation being terminated too soon, the information on the Microcontroller could be read normally. AT89C51 from ATMEL could be a good example, after this flaws have been found by MCU reader in the late 1990, ATMEL redesign the schematic diagram of MCU to increase its anti-read MCU capability.