ST AN671 Application note

AN671

Application note

Prevention of data corruption in ST6 on-chip EEPROM

INTRODUCTION

The ST6 Microcontroller has been designed to avoid any potential corruption of data programmed into its on-chip EEPROM (when available). Data integrity can be ensured as long as the application designer follows the guidelines provided in this note.

In general, EEPROM data corruption occurs whenever the reset signal is not controlled when the power supply goes up or down.

This is particularly true with a slow ramp-up and/or slow fall time of the power supply, since the device may be in a supply voltage area where the device functionality is not guaranteed for a long time.

If no special care is taken during the power up sequence regarding the reset signal then the microcontroller core may start writing into the EEPROM. The same behaviour may occur upon a power down.

Two complementary solutions are possible to prevent from these unwanted actions, a software solution and a hardware solution.

1 SOFTWARE SOLUTION

This solution only applies to the power down sequence which represents the majority of data corruption risks.

The solution consists in disabling the enable bit of the EEPROM control register after writing into the EEPROM and before switching "off" the application; this avoids any spurious writing as described above.

Note that this bit is automatically reset upon power on, thus the reason why most cases of data corruption can occur at power down, as the enable bit may have been modified by the user software.

August 2008

Rev 2

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PREVENTION OF DATA CORRUPTION IN ST6 ON-CHIP EEPROM

2 HARDWARE SOLUTION

No problems can occur when the device is in the reset state as long as the voltage has not reached the minimum value at which the CPU performs. A simple level detection circuit which forces the reset input low before reaching this critical point prevents any unwanted writing into the EEPROM.

Figure 1. Reset Network

Reset Pin

Figure 2. Supply/ Reset graph

Vdd max.

Min operating voltage

Reset Pin

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