參數(shù)資料
型號: AT89LP428-20PU
廠商: Atmel
文件頁數(shù): 8/149頁
文件大?。?/td> 0K
描述: MCU 8051 4K FLASH SPI 28PDIP
產(chǎn)品培訓(xùn)模塊: MCU Product Line Introduction
標(biāo)準(zhǔn)包裝: 14
系列: 89LP
核心處理器: 8051
芯體尺寸: 8-位
速度: 20MHz
連通性: SPI,UART/USART
外圍設(shè)備: 欠壓檢測/復(fù)位,POR,PWM,WDT
輸入/輸出數(shù): 30
程序存儲器容量: 4KB(4K x 8)
程序存儲器類型: 閃存
EEPROM 大小: 512 x 8
RAM 容量: 768 x 8
電壓 - 電源 (Vcc/Vdd): 2.4 V ~ 5.5 V
振蕩器型: 內(nèi)部
工作溫度: -40°C ~ 85°C
封裝/外殼: 28-DIP(0.300",7.62mm)
包裝: 管件
105
3654A–MICRO–8/09
AT89LP428/828
19. Programmable Watchdog Timer
The programmable Watchdog Timer (WDT) protects the system from incorrect execution by trig-
gering a system reset when it times out after the software has failed to feed the timer prior to the
timer overflow. By Default the WDT counts CPU clock cycles. The prescaler bits, PS0, PS1 and
PS2 in SFR WDTCON are used to set the period of the Watchdog Timer from 16K to 2048K
clock cycles. The Timer Prescaler can also be used to lengthen the time-out period (see Table
6-2 on page 23) The WDT is disabled by Reset and during Power-down mode. When the WDT
times out without being serviced, an internal RST pulse is generated to reset the CPU. See
Table 19-1 for the available WDT period selections.
Note:
1. The WDT time-out period is dependent on the system clock frequency.
The Watchdog Timer consists of a 14-bit timer with 7-bit programmable prescaler. Writing the
sequence 1EH/E1H to the WDTRST register enables the timer. When the WDT is enabled, the
WDTEN bit in WDTCON will be set to “1”. To prevent the WDT from generating a reset when if
overflows, the watchdog feed sequence must be written to WDTRST before the end of the time-
out period. To feed the watchdog, two write instructions must be sequentially executed success-
fully. Between the two write instructions, SFR reads are allowed, but writes are not allowed. The
instructions should move 1EH to the WDTRST register and then 1EH to the WDTRST register.
An incorrect feed or enable sequence will cause an immediate watchdog reset. The program
sequence to feed or enable the watchdog timer is as follows:
MOV WDTRST, #01Eh
MOV WDTRST, #0E1h
Table 19-1.
Watchdog Timer Time-out Period Selection
WDT Prescaler Bits
Period(1)
(Clock Cycles)
PS2
PS1
PS0
000
16K
001
32K
010
64K
011
128K
100
256K
101
512K
1
0
1024K
1
2048K
Time-out Period
2
PS
14
+
()
Oscillator Frequency
-------------------------------------------------------
TPS
1
+
()
×
=
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