单片机可以看成是在时钟驱动下的时序逻辑电路,单片机工作过程中,所有的工作都是在时钟信号控制下进行的.针对MCU的硬件监控技术及复位系统,依据单稳态结构特性,设计一款时钟丢失检测电路.该电路采用电流源取代电阻的方式,实现单稳态电路的阻容结构.电路上电使能后,监测时钟上升沿,通过时钟上升沿的触发,使电路保持单稳态工作状态.采用0.25μm CMOS工艺进行仿真,仿真结果显示,如果时钟保持在高电平或低电平的时间大于258.4μs时,单稳态电路将超时,并产生一个复位信号.此电路结构简单,便于集成在MCU复位系统,可对系统时钟进行丢失监测.%Single-chip microcontroller may be regarded as the sequential logic circuit driven by clock, in which all the work was conducted under the clock signal control.According to the hardware mon-itoring technology of MCU and reset system, a missing clock detector circuit based on the structural char-acteristics of monostable is designed ,which uses the current source to replace the resistance, and realizes the resistance-capacitance structure of the monostable circuit. After the circuit being powered on, clock rising edge is monitored, which maintains a monostable working state by triggering the clock rising edge. Using the 0.25μm CMOS technology to the simulation, the simulation results show that if the time of the clock holding in high level or low level is greater than 258.4μs, the monostable circuit will time out, and generate a reset singal. The circuit structure is simple, which is easy to integrate in the MCU reset system and can monitor the system missing clock.
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