ST10F296 datasheet(212/346 Pages) STMICROELECTRONICS

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Watchdog timer

ST10F296E

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The PONR flag of the WDTCON register is set if the output voltage of the internal 1.8 V

supply falls below the threshold of the power-on detection circuit (typically 1.5 V). This circuit

can detect major failures of the external 5 V supply, but, if the internal 1.8 V supply does not

drop below 1.5 V, the PONR flag is not set.

This could occur with a fast switch off/switch on of the 5 V supply. The time needed for such

a sequence to activate the PONR flag depends on the value of the capacitors connected to

the supply and on the exact value of the internal threshold of the detection circuit.

Table 127.

WDTCON register description

Bit

Bit name

Function

15-8

WDTREL

Watchdog reload value

5PONR(1)(2)(3)

More than one reset indication flag may be set. After EINIT, all flags are cleared.

Power-on is detected when a rising edge from V18 = 0 V to V18 > 1.5 V is recognized on the internal 1.8 V

supply.

Bit cannot be modified directly by software.

Power-on (asynchronous) reset indication flag

Set by the input RSTIN if a power-on condition has been detected.

Cleared by the EINIT instruction.

4LHWR(1)(2)(3)

Long hardware reset indication flag

Set by the input RSTIN. Cleared by the EINIT instruction.

3SHWR(1)(2)(3)

Short hardware reset indication flag

Set by the input RSTIN. Cleared by the EINIT instruction.

2SWR(1)(2)(3)

Software reset indication flag

Set by the SRST execution. Cleared by the EINIT instruction.

1WDTR(1)(2)(3)

Watchdog timer reset indication flag

Set by the watchdog timer on an overflow. Cleared by a hardware reset

or by the SRVWDT instruction.

0WDTIN

Watchdog timer input frequency selection

0: Input frequency is fCPU/2.

1: Input frequency is fCPU/128.

Table 128.

WDTCON bit values on different resets

Reset source

PONR

LHWR

SHWR

SWR

WDTR

Power-on reset

Power-on after partial supply

failure

(1)(2)

PONR bit cannot be set because of a short supply failure.

For power-on reset and resets after supply partial failure, asynchronous resets must be used.

Long hardware reset

Short hardware reset

Software reset

Watchdog reset

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