AN3029 datasheet(14/42 Pages) STMICROELECTRONICS

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Reset control

AN3029

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DocID16139 Rev 5

Reset control

5.1

Reset management overview

The reset pin is a 3.3 V bidirectional I/O. After startup it can be programmed by software to

be used as a general purpose I/O.

Its output buffer driving capability is fixed to IolMIN = 2 mA @ 0.45 V in the 1.8 V to 3.6 V

range which includes a ~45 k pull-up. Output buffer is reduced to the n-channel MOSFET

(NMOS). The receiver includes a glitch filter, whereas the output buffer includes a 20 µs

delay.

There are many reset sources, including:

•

External reset through the NRST pin

•

Power-on reset (POR) and brown-out reset (BOR): During power-on, the POR keeps

the device under reset until the supply voltage (VDD and VDDx) reach the voltage level

at which level the BOR starts to function. STM8L101xx devices have only a POR.

•

Independent watchdog reset (IWDG)

•

Window watchdog reset (WWDG), featuring also software reset: only for STM8L05xx,

STM8L15xxx, STM8L162xx, STM8AL31xx, and STM8AL3Lxx.

•

SWIM reset: An external device connected to the SWIM interface can request the

SWIM block to generate a microcontroller reset.

•

Illegal opcode reset: If a code to be executed does not correspond to any opcode or

prebyte value, a reset is generated.

Figure 7 shows a simplified functional I/O reset schematic.

Figure 7. Reset management

RPU

System reset

Filter

100 nF

External

reset circuit

NRST

ai14866d

Illegal op code reset

Swim reset

POR/BOR reset

IWDG/WWDG/software reset

Delay

STM8

VDD_IO

Pulse

generator

(min 20 μs)

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