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42
AT89C51RB2/RC2
4180E–8051–10/06
Pulse Width Modulator
Mode
All of the PCA Modules can be used as PWM outputs. Figure 16 shows the PWM func-
tion. The frequency of the output depends on the source for the PCA timer. All of the
Modules will have the same frequency of output because they all share the PCA timer.
The duty cycle of each Module is independently variable using the module's capture
register CCAPLn. When the value of the PCA CL SFR is less than the value in the mod-
ule's CCAPLn SFR the output will be low, when it is equal to or greater than the output
will be high. When CL overflows from FF to 00, CCAPLn is reloaded with the value in
CCAPHn. This allows updating the PWM without glitches. The PWM and ECOM bits in
the module's CCAPMn register must be set to enable the PWM mode.
Figure 16. PCA PWM Mode
PCA Watchdog Timer
An on-board watchdog timer is available with the PCA to improve the reliability of the
system without increasing chip count. Watchdog timers are useful for systems that are
susceptible to noise, power glitches, or electrostatic discharge. Module 4 is the only
PCA Module that can be programmed as a watchdog. However, this Module can still be
used for other modes if the watchdog is not needed. Figure 14 shows a diagram of how
the watchdog works. The user pre-loads a 16-bit value in the compare registers. Just
like the other compare modes, this 16-bit value is compared to the PCA timer value. If a
match is allowed to occur, an internal reset will be generated. This will not cause the
RST pin to be driven high.
In order to hold off the reset, the user has the following three options:
1.
Periodically change the compare value so it will never match the PCA timer.
2.
Periodically change the PCA timer value so it will never match the compare
values.
3.
Disable the watchdog by clearing the WDTE bit before a match occurs and then
re-enable it.
The first two options are more reliable because the watchdog timer is never disabled as
in option #3. If the program counter ever goes astray, a match will eventually occur and
cause an internal reset. The second option is also not recommended if other PCA Mod-
ules are being used. Remember, the PCA timer is the time base for all modules;
CL
CCAPnH
CCAPnL
ECOMn
CCAPMn, n = 0 to 4
0xDA to 0xDE
CAPNn MATn TOGn PWMn ECCFn
CAPPn
8-bit Comparator
CEXn
“0”
“1”
Enable
PCA Counter/Timer
Overflow
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AT89C51RB2-3CSUL
功能描述:8位微控制器 -MCU 8-bit 16K Flash C51RB2 RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT
AT89C51RB2-3CSUM
功能描述:8位微控制器 -MCU C51RB2 FLASH 5V 16k ind RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT
AT89C51RB2L1-RLTUL
功能描述:8位微控制器 -MCU Microcontroller
RoHS:否 制造商:Silicon Labs 核心:8051 处理器系列:C8051F39x 数据总线宽度:8 bit 最大时钟频率:50 MHz 程序存储器大小:16 KB 数据 RAM 大小:1 KB 片上 ADC:Yes 工作电源电压:1.8 V to 3.6 V 工作温度范围:- 40 C to + 105 C 封装 / 箱体:QFN-20 安装风格:SMD/SMT
AT89C51RB2-RLRIL
功能描述:IC MCU FLASH 8051 16K 3V 44-VQFP RoHS:否 类别:集成电路 (IC) >> 嵌入式 - 微控制器， 系列:89C 标准包装:1,500 系列:AVR® ATtiny 核心处理器:AVR 芯体尺寸:8-位 速度:16MHz 连通性:I²C，LIN，SPI，UART/USART，USI 外围设备:欠压检测/复位，POR，PWM，温度传感器，WDT 输入/输出数:16 程序存储器容量:8KB（4K x 16） 程序存储器类型:闪存 EEPROM 大小:512 x 8 RAM 容量:512 x 8 电压 - 电源 (Vcc/Vdd):2.7 V ~ 5.5 V 数据转换器:A/D 11x10b 振荡器型:内部 工作温度:-40°C ~ 125°C 封装/外壳:20-SOIC（0.295"，7.50mm 宽） 包装:带卷 (TR)
AT89C51RB2-RLRIM
功能描述:IC MCU FLASH 8051 16K 5V 44-VQFP RoHS:否 类别:集成电路 (IC) >> 嵌入式 - 微控制器， 系列:89C 产品培训模块:MCU Product Line Introduction
AVR® UC3 Introduction 标准包装:2,500 系列:AVR®32 UC3 B 核心处理器:AVR 芯体尺寸:32-位 速度:60MHz 连通性:I²C，IrDA，SPI，SSC，UART/USART，USB 外围设备:欠压检测/复位，DMA，POR，PWM，WDT 输入/输出数:28 程序存储器容量:128KB（128K x 8） 程序存储器类型:闪存 EEPROM 大小:- RAM 容量:32K x 8 电压 - 电源 (Vcc/Vdd):1.65 V ~ 1.95 V 数据转换器:A/D 6x10b 振荡器型:内部 工作温度:-40°C ~ 85°C 封装/外壳:48-TQFP 包装:带卷 (TR) 配用:ATSTK600-TQFP48-ND - STK600 SOCKET/ADAPTER 48-TQFPATAVRONEKIT-ND - KIT AVR/AVR32 DEBUGGER/PROGRMMRATEVK1101-ND - KIT DEV/EVAL FOR AVR32 AT32UC3B 其它名称:AT32UC3B1128-AUR-NDAT32UC3B1128-AURTR
AT89C51RB2-RLRUL
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AT89C51RB2-RLRUM
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AT89C51RB2-RLTCM
制造商:ATMEL 制造商全称:ATMEL Corporation 功能描述:8-bit Microcontroller with 16K/ 32K Bytes Flash