ST72F324BJ STMICROELECTRONICS [STMicroelectronics], ST72F324BJ Datasheet - Page 60

• Manufacturer Part Number: ST72F324BJ
• Description: 8-bit MCU, 3.8 to 5.5 V operating range with 8 to 32 Kbyte Flash/ROM, 10-bit ADC, 4 timers, SPI, SCI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

On-chip peripherals
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On-chip peripherals
Watchdog timer (WDG)
Introduction
The Watchdog timer is used to detect the occurrence of a software fault, usually generated
by external interference or by unforeseen logical conditions, which causes the application
program to abandon its normal sequence. The Watchdog circuit generates an MCU reset on
expiry of a programmed time period, unless the program refreshes the counter’s contents
before the T6 bit becomes cleared.
Main features
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Functional description
The counter value stored in the Watchdog Control register (WDGCR bits T[6:0]), is
decremented every 16384 f
be programmed by the user in 64 increments.
If the watchdog is activated (the WDGA bit is set) and when the 7-bit timer (bits T[6:0]) rolls
over from 40h to 3Fh (T6 becomes cleared), it initiates a reset cycle pulling low the reset pin
for typically 30µs.
The application program must write in the WDGCR 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 WDGCR register must be
between FFh and C0h:
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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 generates a reset.
Programmable free-running downcounter
Programmable reset
Reset (if Watchdog activated) when the T6 bit reaches zero
Optional reset on HALT instruction (configurable by option byte)
Hardware Watchdog selectable by option byte
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 (see
The timing varies between a minimum and a maximum value due to the unknown
status of the prescaler when writing to the WDGCR register (see
OSC2
cycles (approx.), and the length of the timeout period can
Figure 33: Approximate timeout
Figure
34).
ST72324B
duration).