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ST72124J2 View Datasheet(PDF) - STMicroelectronics

Part Name
Description
MFG CO.
'ST72124J2' PDF : 150 Pages View PDF
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
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
Figure 28. Watchdog Block Diagram
Hardware Watchdog selectable by option byte
Watchdog Reset indicated by status flag (in
versions with Safe Reset option only)
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.
RESET
WDGA T6
WATCHDOG CONTROL REGISTER (CR)
T5 T4 T3 T2 T1 T0
7-BIT DOWNCOUNTER
fCPU
CLOCK DIVIDER
÷12288
50/150
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