ST10F273Z4 Datasheet, PDF (78/188 Pages) STMicroelectronics – 16-bit MCU with 512 Kbyte Flash memory and 36 Kbyte RAM

Watchdog timer
19 Watchdog timer
ST10F273Z4
The watchdog timer is a fail-safe mechanism which prevents the microcontroller from
malfunctioning for long periods of time.
The watchdog timer is always enabled after a reset of the chip and can only be disabled in
the time interval until the EINIT (end of initialization) instruction has been executed.
Therefore, the chip start-up procedure is always monitored. The software must be designed
to service the watchdog timer before it overflows. If, due to hardware or software related
failures, the software fails to do so, the watchdog timer overflows and generates an internal
hardware reset. It pulls the RSTOUT pin low in order to allow external hardware components
to be reset.
Each of the different reset sources is indicated in the WDTCON register:
● Watchdog timer reset in case of an overflow
● Software Reset in case of execution of the SRST instruction
● Short, long and power-on reset in case of hardware reset (and depending of reset
pulse duration and RPD pin configuration)
The indicated bits are cleared with the EINIT instruction. The source of the reset can be
identified during the initialization phase.
The watchdog timer is 16-bit, clocked with the system clock divided by 2 or 128. The high
Byte of the watchdog timer register can be set to a pre-specified reload value (stored in
WDTREL).
Each time it is serviced by the application software, the high byte of the watchdog timer is
reloaded. For security, rewrite WDTCON each time before the watchdog timer is serviced
The Table 48 and Table 49 show the watchdog time range for 40 MHz and 64 MHz CPU
clock respectively.
Table 48. WDTREL reload value (f_CPU = 40 MHz)
Reload value in WDTREL
Prescaler for f_CPU = 40 MHz
2 (WDTIN = ‘0’)
128 (WDTIN = ‘1’)
FFh
12.8µs
819.2µs
00h
3.277ms
209.7ms
Table 49. WDTREL reload value (f_CPU = 64 MHz)
Reload value in WDTREL
Prescaler for f_CPU = 64 MHz
2 (WDTIN = ‘0’)
128 (WDTIN = ‘1’)
FFh
8µs
512µs
00h
2.048ms
131.1ms
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