参数资料
型号: ST72311R9T3/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PQFP64
封装: 14 X 14 MM, TQFP-64
文件页数: 97/152页
文件大小: 1909K
代理商: ST72311R9T3/XXX
ST72311R, ST72511R, ST72532R
49/152
10 ON-CHIP PERIPHERALS
10.1 WATCHDOG TIMER (WDG)
10.1.1 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.
10.1.2 Main Features
s
Programmable timer (64 increments of 12288
CPU cycles)
s
Programmable reset
s
Reset (if watchdog activated) after a HALT
instruction or when the T6 bit reaches zero
s
Hardware Watchdog selectable by option byte
s
Watchdog Reset indicated by status flag (in
versions with Safe Reset option only)
10.1.3 Functional Description
The counter value stored in the CR register (bits
T[6:0]), is decremented every 12,288 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 typically
500ns.
Figure 28. Watchdog Block Diagram
RESET
WDGA
7-BIT DOWNCOUNTER
fCPU
T6
T0
CLOCK DIVIDER
WATCHDOG CONTROL REGISTER (CR)
÷12288
T1
T2
T3
T4
T5
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