ST6215CB3 datasheet(19/70 Pages) STMICROELECTRONICS

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ST62T15C/T25C/E25C

RESETS (Cont’d)

3.2.3 Watchdog Reset

The MCU provides a Watchdog timer function in

order to ensure graceful recovery from software

upsets. If the Watchdog register is not refreshed

before an end-of-count condition is reached, the

internal reset will be activated. This, amongst oth-

er things, resets the watchdog counter.

The MCU restarts just as though the Reset had

been generated by the RESET pin, including the

built-in stabilisation delay period.

3.2.4 LVD Reset

The on-chip Low Voltage Detector, selectable as

user option, features static Reset when supply

voltage is below a reference value. Thanks to this

feature, external reset circuit can be removed

while keeping the application safety. This SAFE

RESET is effective as well in Power-on phase as

in power supply drop with different reference val-

ues, allowing hysteresis effect. Reference value in

case of voltage drop has been set lower than the

reference value for power-on in order to avoid any

parasitic Reset when MCU start’s running and

sinking current on the supply.

As long as the supply voltage is below the refer-

ence value, there is a internal and static RESET

command. The MCU can start only when the sup-

ply voltage rises over the reference value. There-

fore, only two operating mode exist for the MCU:

RESET active below the voltage reference, and

running mode over the voltage reference as

shown on the Figure 14, that represents a power-

up, power-down sequence.

Note: When the RESET state is controlled by one

of the internal RESET sources (Low Voltage De-

tector, Watchdog, Power on Reset), the RESET

pin is tied to low logic level.

Figure 14. LVD Reset on Power-on and Power-down (Brown-out)

3.2.5 Application Notes

No external resistor is required between VDD and

the Reset pin, thanks to the built-in pull-up device.

Direct external connection of the pin RESET to

VDD must be avoided in order to ensure safe be-

haviour of the internal reset sources (AND.Wired

structure).

RESET

VR02106A

time

VUp

Vdn

VDD

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