ST10F269Z2QX datasheet(107/161 Pages) STMICROELECTRONICS

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18 - SYSTEM RESET

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

system start-up configuration is different for each case as shown in Table 28.

Table 28 : Reset Event Definition

18.1 - Long Hardware Reset

The reset is triggered when RSTIN pin is pulled low, then the MCU is immediately forced in reset default

state. It pulls low RSTOUT pin, it cancels pending internal hold states if any, it aborts external bus cycle, it

switches buses (data, address and control signals) and I/O pin drivers to high-impedance, it pulls high PORT0

pins and the reset sequence starts.

To get a long hardware reset, the duration of the external RSTIN signal must be longer than 1040 TCL.

The level of RPD pin is sampled during the whole RSTIN pulse duration. A low level on RPD pin

determines an asynchronous reset while a high level leads to a synchronous reset.

Note

A reset can be entered as synchronous and exit as asynchronous if VRPD voltage drops below the

RPD pin threshold (typically 2.5V for VDD = 5V) when RSTIN pin is low or when RSTIN pin is

internally pulled low.

18.1.1 - Asynchronous Reset

Figure 54 and Figure 55 show asynchronous reset condition (RPD pin is at low level).

Figure 54 : Asynchronous Reset Sequence External Fetch

Note: 1) RSTIN rising edge to internal latch of PORT0 is 3 CPU clock cycles (6 TCL) if the PLL is bypassed and the prescaler is on

(fCPU =fXTAL / 2), else it is 4 CPU clock cycles (8 TCL).

Reset Source

Short-cut

Conditions

Power-on reset

PONR

Power-on

Long Hardware reset (synchronous & asynchronous)

LHWR

t RSTIN > 1040 TCL

Short Hardware reset (synchronous reset)

SHWR

4 TCL < t RSTIN < 1038 TCL

Watchdog Timer reset

WDTR

WDT overflow

Software reset

SWR

SRST execution

6 or 8 TCL1)

CPU Clock

RSTIN

Asynchronous

Reset Condition

RPD

RSTOUT

ALE

PORT0

Reset Configuration

1st Instruction External Fetch

Latching point of PORT0

for system start-up

configuration

EXTERNAL FETCH

Internal reset

5 TCL

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