ST72C334J4TAE STMicroelectronics, ST72C334J4TAE Datasheet - Page 50

• Manufacturer Part Number: ST72C334J4TAE
• Description: 8-bit MCU for automotive with single voltage Flash/ROM memory, ADC, 16-bit timers, SPI, SCI interfaces
• Manufacturer: STMicroelectronics

ST72334xx-Auto, ST72314xx-Auto, ST72124Jx-Auto
13 ON-CHIP PERIPHERALS
13.1 WATCHDOG TIMER (WDG)
13.1.1 Introduction
The Watchdog timer is used to detect the occur-
rence of a software fault, usually generated by ex-
ternal interference or by unforeseen logical condi-
tions, which causes the application program to
abandon its normal sequence. The Watchdog cir-
cuit generates an MCU reset on expiry of a pro-
grammed time period, unless the program refresh-
es the counter’s contents before the T6 bit be-
comes cleared.
13.1.2 Main Features
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■
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Figure 28. Watchdog Block Diagram
50/150
Programmable timer (64 increments of 12288
CPU cycles)
Programmable reset
Reset (if watchdog activated) after a HALT
instruction or when the T6 bit reaches zero
f
CPU
WDGA
RESET
T6
T5
WATCHDOG CONTROL REGISTER (CR)
7-BIT DOWNCOUNTER
CLOCK DIVIDER
T4
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13.1.3 Functional Description
The counter value stored in the CR register (bits
T[6:0]), is decremented every 12288 machine cy-
cles, and the length of the timeout period can 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 typical-
ly 30µs.
÷12288
Hardware Watchdog selectable by option byte
Watchdog Reset indicated by status flag (in
versions with Safe Reset option only)
T3
T2
T1
T0