参数资料
型号: ST7263BK1B/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, PDIP32
封装: 0.400 INCH, LEAD FREE, SHRINK, PLASTIC, DIP-32
文件页数: 73/140页
文件大小: 1423K
代理商: ST7263BK1B/XXX
ST7263B
38/140
11 ON-CHIP PERIPHERALS
11.1 WATCHDOG TIMER (WDG)
11.1.1 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.
11.1.2 Main Features
Programmable
free-running
counter
(64
increments of 49,152 CPU cycles)
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.
11.1.3 Functional Description
The counter value stored in the CR register (bits
T6:T0), is decremented every 49,152 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 T6:T0) rolls over
from 40h to 3Fh (T6 becomes cleared), it initiates
a reset cycle pulling low the reset pin for typically
30s.
The application program must write in the CR reg-
ister 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 CR register
must be between FFh and C0h (see Table 16, ".
– The WDGA bit is set (watchdog enabled)
– The T6 bit is set to prevent generating an imme-
diate reset
– The T5:T0 bits contain the number of increments
which represents the time delay before the
watchdog produces a reset.
Figure 25. Watchdog Block Diagram
RESET
WDGA
7-BIT DOWNCOUNTER
fCPU
T6
T0
CLOCK DIVIDER
WATCHDOG CONTROL REGISTER (CR)
÷49152
T1
T2
T3
T4
T5
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