ST7LITE49M datasheet(78/188 Pages) STMICROELECTRONICS

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On-chip peripherals

ST7LITE49M

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The application program must write in the CR register at regular intervals during normal

operation to prevent an MCU reset. This downcounter is free-running: it counts down even if

the watchdog is disabled. The value to be stored in the CR register must be between FFh

and C0h (see Table 32: Watchdog timing):

●

The WDGA bit is set (watchdog enabled)

●

The T6 bit is set to prevent generating an immediate reset

●

The T[5:0] bits contain the number of increments which represents the time delay

before the watchdog produces a reset.

Following a reset, the watchdog is disabled. Once activated it cannot be disabled, except by

a reset.

The T6 bit can be used to generate a software reset (the WDGA bit is set and the T6 bit is

cleared).

If the watchdog is activated, the HALT instruction will generate a Reset.

11.1.4

Hardware watchdog option

If Hardware Watchdog is selected by option byte, the watchdog is always active and the

WDGA bit in the CR is not used.

Refer to the option byte description in Section 14 on page 175.

Using Halt mode with the WDG (WDGHALT option)

If Halt mode with Watchdog is enabled by option byte (No watchdog reset on HALT

instruction), it is recommended before executing the HALT instruction to refresh the WDG

counter, to avoid an unexpected WDG reset immediately after waking up the microcontroller.

Same behaviour in active-halt mode.

11.1.5

Interrupts

None.

Table 32.

Watchdog timing(1)(2)

The timing variation shown in Table 32 is due to the unknown status of the prescaler when writing to the

CR register.

The number of CPU clock cycles applied during the Reset phase (256 or 4096) must be taken into account

in addition to these timings.

fCPU = 8MHz

WDG

counter code

min

[ms]

max

[ms]

C0h

FFh

127

128

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