2/11

UPGRADING FROM ST625X/6XB TO ST625X/6XC

1 SILICON CHANGES

1.1 NEW FEATURES

1.1.1 LOW VOLTAGE DETECTOR (LVD)

ST625X/6XC now features an on-chip Low Voltage Detector which is enabled by setting a bit

in the option bytes (refer to the Option Bytes section in the device data sheet).

The LVD allows the device to be used without any external RESET circuitry. In this case, the

RESET pin should be left unconnected. When the LVD is not activated, an external circuit is

mandatory to ensure correct Power On Reset operation. For more details, please refer to the

application note AN669.

The LVD generates a static Reset when the supply voltage is below a reference value. This

means that it secures the power-up as well as the power-down keeping the ST6 in reset.

The V

in order to avoid a parasitic reset when the MCU starts running and sinks current on the supply

– V

– V

The LVD function is illustrated in Figure 1.

If the LVD is enabled, the MCU can be in only one of two states:

– Over the input threshold voltage, it is running under full software control

– Below the input threshold voltage, it is in static safe reset

In these conditions, secure operation is guaranteed without the need for external reset hard-

ware.

During a Low Voltage Detector Reset, the RESET pin is held low, thus permitting the MCU to

reset other devices.

2