參數(shù)資料
型號： VMX51C900
廠商： Electronic Theatre Controls, Inc.
英文描述： Versa Mix 8051 MCU with LCD Controller and ADC
中文描述： 8051反之亦然混合與LCD控制器和ADC的微控制器
文件頁數(shù)： 41/55頁
文件大小： 2395K
代理商： VMX51C900
VMX51C900
______________________________________________________________________________________________
www.ramtron.com
page 41 of 55
The Watchdog Timer
The VMX51C900 watchdog timer (WDT) is a 16-bit
free-running counter operating from an independent
250KHz internal RC oscillator. An overflow of the WDT
counter will reset the processor.
The WDT is a useful safety measure for systems that
are susceptible to noise, power glitches and other
conditions that could cause the software to go into
infinite dead loops or runaways. The WDT provides the
user software with a recovery mechanism from
abnormal software conditions.
Watchdog Timer Registers
The configuration and use of the VMX51C900
watchdog timer is handled by three registers:
WDTKEY, WDTCTRL and SYSCON.
The WDTKEY register ensures that the watchdog timer
is not inadvertently reset in case of program
malfunction.
The WDTCTRL register is by default configured as a
read-only register. To modify its contents, two
consecutive write operations to the WDTKEY register
must be performed as follows:
MOV WDTKEY,#01Eh
MOV
WDTKEY,#0E1h
Once the configuration or WDT reset operation is
complete, the WDTCTRL register can be restored to
read-only by writing the following sequence into the
WDTKEY register:
MOV WDTKEY,#0E1h
MOV
WDTKEY,#01Eh
T
ABLE
51:
W
ATCH
D
OG
T
IMER
K
EY REGISTER
:
WDTKEY
–
SFR
97
H
7
6
5
4
3
2
1
0
WDTKEY7:0
Bit
7:0
Mnemonic
WDTKEY
Description
Watchdog Key
Once the WDT is enabled, the user software must
clear it periodically. If the WDT is not cleared, its
overflow will trigger a reset of the VMX51C900.
T
ABLE
52:
W
ATCH
D
OG
T
IMER
R
EGISTERS
:
WDTCTRL
–
SFR
9F
H
7
6
WDT
CLR
Bit
Mnemonic
7
WDTE
6
Unused
5
WDTCLR
[4:3]
Unused
2
WDTPS2
1
WDTPS1
0
WDTPS0
The WDT timeout delay can be adjusted by configuring
the clock divider input for the WDT time base source
clock.
To
select
the
[WDTPS2~WDTPS0] bits of the watchdog timer
control register should be set accordingly.
The following table indicates the approximate timeout
periods for different values of the WDTPSx bits of the
watchdog timer register.
T
ABLE
53:
T
IMEOUT
P
ERIOD AT
5
4
3
2
1
0
WDTE
Unused
Unused
WDT
PS2
WDT
PS1
WDT
PS0
Description
Watchdog Timer Enable Bit
-
Watchdog Timer Counter Clear Bit
-
Clock Source Divider Bit 2
Clock Source Divider Bit 1
Clock Source Divider Bit 0
divider
value,
the
WDTPS [2:0]
WDT Period
000
2.048ms
001
4.096ms
010
011
8.192ms
16.384ms
100
32.768ms
101
110
111
65.536ms
131.072ms
262.144ms
To enable the WDT, bit 7 (WDTE) of the WDTCTRL
register must be set to 1. The 16-bit counter will then
begin counting from the 250KHz oscillator divided,
according to the value of the WDTPS2~WDTPS0 bits.
The WDT is cleared by setting the WDTCLR bit of the
WDTCTRL to 1. This will clear the contents of the 16-
bit counter and force it to restart.
If the WDT overflows, the processor will be reset, the
WDR bit (7) of the SYSCON register will be set to 1
and the WDTE bit will be cleared to 0. The user should
check the WDR bit if an unexpected reset has taken
place.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
VMX51C900-25-L 功能描述:8位微控制器 -MCU 8K+256 25MHz 5V RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
VMX51C900-25-LG 功能描述:8位微控制器 -MCU 8K+256 25MHz 5V RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
VMX51C900-25-L-G 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Versa Mix 8051 MCU with LCD Controller and ADC
VMX51C900-25-P 功能描述:8位微控制器 -MCU 8K+256 25MHz 5V RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
VMX51C900-25-PG 功能描述:8位微控制器 -MCU 8K+256 25MHz 5V RoHS:否 制造商:Silicon Labs 核心:8051 處理器系列:C8051F39x 數(shù)據(jù)總線寬度:8 bit 最大時鐘頻率:50 MHz 程序存儲器大小:16 KB 數(shù)據(jù) RAM 大小:1 KB 片上 ADC:Yes 工作電源電壓:1.8 V to 3.6 V 工作溫度范圍:- 40 C to + 105 C 封裝 / 箱體:QFN-20 安裝風(fēng)格:SMD/SMT
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