CD00001237 datasheet(25/105 Pages) STMICROELECTRONICS

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ST6215C ST6225C

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RESET (Cont’d)

5.3.3 RESET Pin

The RESET pin may be connected to a device on

the application board in order to reset the MCU if

required. The RESET pin may be pulled low in

RUN, WAIT or STOP mode. This input can be

used to reset the internal state of the MCU and en-

sure it starts-up correctly. The pin, which is con-

nected to an internal pull-up, is active low and fea-

tures a Schmitt trigger input. A delay (2048 clock

cycles) added to the external signal ensures that

even short pulses on the RESET pin are accepted

as valid, provided VDD has completed its rising

phase and that the oscillator is running correctly

(normal RUN or WAIT modes). The MCU is kept in

the Reset state as long as the RESET pin is held

low.

If the RESET pin is grounded while the MCU is in

RUN or WAIT modes, processing of the user pro-

gram is stopped (RUN mode only), the I/O ports

are configured as inputs with pull-up resistors and

the main oscillator is restarted. When the level on

the RESET pin then goes high, the initialization se-

quence is executed at the end of the internal delay

period.

If the RESET pin is grounded while the MCU is in

STOP mode, the oscillator starts up and all the I/O

ports are configured as inputs with pull-up resis-

tors. When the RESET pin level then goes high,

the initialization sequence is executed at the end

of the internal delay period.

A simple external RESET circuitry is shown in Fig-

ure 15. For more details, please refer to the appli-

cation note AN669.

Figure 14. Reset Block Diagram

fINT

RESET

WATCHDOG RESET

LVD RESET

INTERNAL

RESET

RESD

1) Resistive ESD protection.

VDD

RPU

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