System reset. STMicroelectronics 16-bit MCU

System reset ST10F271B/ST10F271E

System reset initializes the MCU in a predefined state. There are six ways to activate a reset

state. The system start-up configuration is different for each case as shown in

Table 48

.

Table 48.

Reset event definition

Reset Source

Power-on reset

Asynchronous Hardware reset

Synchronous Long Hardware reset

Synchronous Short Hardware reset

Watchdog Timer reset

Software reset

Flag

PONR

LHWR

SHWR

WDTR

SWR

RPD

Status

Low

Low

High

High

3)

3)

Conditions

Power-on t

RSTIN

>

1) t

RSTIN

> (1032 + 12) TCL + max(4 TCL,

500ns) t

RSTIN

> max(4 TCL, 500ns) t

RSTIN

≤

500ns)

WDT overflow

SRST instruction execution

1)

RSTIN pulse should be longer than 500ns (Filter) and than settling time for configuration of Port0.

2)

Section 20.1

for more details on minimum reset pulse duration.

3)

The RPD status has no influence unless Bidirectional Reset is activated (bit BDRSTEN in SYSCON): RPD low inhibits the Bidirectional reset on SW and WDT reset events, that is RSTIN is not activated (refer to

Sections 20.4

,

20.5

and

20.6

).

On RSTIN input pin an on-chip RC filter is implemented. It is sized to filter all the spikes shorter than 50ns. On the other side, a valid pulse shall be longer than 500ns to grant that

ST10 recognizes a reset command. In between 50ns and 500ns a pulse can either be filtered or recognized as valid, depending on the operating conditions and process variations.

For this reason all minimum durations mentioned in this Chapter for the different kind of reset events shall be carefully evaluated taking into account of the above requirements.

In particular, for Short Hardware Reset, where only 4 TCL is specified as minimum input reset pulse duration, the operating frequency is a key factor. Examples:

● For a CPU clock of 64 MHz, 4 TCL is 31.25ns, so it would be filtered. In this case the Obsolete Product(s) - Obsolete Product(s)

● For a CPU clock of 4 MHz, 4 TCL is 500ns. In this case the minimum from the formula

Obsolete Product(s) - Obsolete Product(s)

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