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ST10F280

System reset

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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 35.

17.1

Asynchronous reset (long hardware reset)

An asynchronous reset is triggered when RSTIN pin is pulled low while RPD pin is at low

level. Then the MCU is immediately forced in reset default state. It pulls low RSTOUT pin, it

cancels pending internal hold states if any, it waits for any internal access cycles to finish, 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.

17.1.1

Power-on reset

The asynchronous reset must be used during the power-on of the MCU. Depending on

crystal frequency, the on-chip oscillator needs about 10ms to 50ms to stabilize. The logic of

the MCU does not need a stabilized clock signal to detect an asynchronous reset, so it is

suitable for power-on conditions. To ensure a proper reset sequence, the RSTIN pin and the

RPD pin must be held at low level until the MCU clock signal is stabilized and the system

configuration value on PORT0 is settled.

17.1.2

Hardware reset

The asynchronous reset must be used to recover from catastrophic situations of the

application. It may be triggerred by the hardware of the application. Internal hardware logic

and application circuitry are described in Reset circuitry chapter and Figure 68, Figure 69

and Figure 66.

17.1.3

Exit of asynchronous reset state

When the RSTIN pin is pulled high, the MCU restarts. The system configuration is latched

from PORT0 and ALE, RD and R/W pins are driven to their inactive level. The MCU starts

program execution from memory location 00'0000h in code segment 0. This starting location

will typically point to the general initialization routine. Timing of asynchronous reset

sequence are summarized in Figure 61.

Table 35.

Reset event definition

Reset source

Short-cut

Conditions

Power-on reset

PONR

Power-on

Long Hardware reset (synchronous & asynchronous)

LHWR

t RSTIN > 1032 TCL

Short Hardware reset (synchronous reset)

SHWR

4 TCL < t RSTIN < 1032 TCL

Watchdog Timer reset

WDTR

WDT overflow

Software reset

SWR

SRST execution

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