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参数资料
型号： ST72SCR1x4T1
厂商： 意法半导体
英文描述： 8-BIT LOW-POWER, FULL-SPEED USB MCU WITH 16K FLASH, 768 RAM, SMARTCARD I/F, TIMER
中文描述： 8位低功耗，全速USB微控制器与16K的闪存，768内存，智能卡的I /楼，计时器
文件页数： 40/102页
文件大小： 1413K
代理商： ST72SCR1X4T1
ST7SCR
40/102
12 ON-CHIP PERIPHERALS
12.1 WATCHDOG TIMER (WDG)
12.1.1 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.
12.1.2 Main Features
I
Programmable timer (64 increments of 65536
CPU cycles)
I
Programmable reset
I
Reset (if watchdog activated) when the T6 bit
reaches zero
I
Hardware Watchdog selectable by option byte
I
Watchdog Reset indicated by status flag
12.1.3 Functional Description
The counter value stored in the CR register (bits
T[6:0]), is decremented every 65,536 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.
The application program must write in the CR reg-
ister at regular intervals during normal operation to
prevent an MCU reset. The value to be stored in
the CR register must be between FFh and C0h
(see
Table 14
):
– The WDGA bit is set (watchdog enabled)
– The T6 bit is set to prevent generating an imme-
diate reset
– The T[5:0] bits contain the number of increments
which represents the time delay before the
watchdog produces a reset.
Table 14.Watchdog Timing (f
CPU
= 8 MHz)
Figure 25. Watchdog Block Diagram
CR Register
initial value
FFh
C0h
WDG timeout period
(ms)
524.288
8.192
Max
Min
RESET
WDGA
7-BIT DOWNCOUNTER
f
CPU
T6
T0
CLOCK DIVIDER
÷
65536
WATCHDOG CONTROL REGISTER (CR)
T1
T2
T3
T4
T5
1
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ST72FSCR1x4T1 8-BIT LOW-POWER, FULL-SPEED USB MCU WITH 16K FLASH, 768 RAM, SMARTCARD I/F, TIMER
ST72PSCR1x4T1 8-BIT LOW-POWER, FULL-SPEED USB MCU WITH 16K FLASH, 768 RAM, SMARTCARD I/F, TIMER
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