《Dean_Conrad_CFREE_ES_RL78_2nd_Ed_dist.pdf》
《0003 RL78_clock_generator.pptx》
《r01uh0146ej0330_rl78g13.pdf》
《r01uh0146cj0320_rl78g13.pdf》
《https://elearning.renesas.com/mod/scorm/view.php?id=294》
Embedded systems consist of computers which are embedded in larger systems. Additional circuitry such as power supplies, clock generators, and reset circuits, are required for the computer to work. Transducers (devices that convert one type of energy into another) are also used to connect microcontrollers to the outside world. There are two classes of transducers: inputs and outputs. Inputs (sensors) include devices such as switches, temperature sensors, keypads, and buttons. Output transducers include devices such as LEDs, motors, and coils.
指令集架构(Instruction Set Architecture)
嵌入式系统由嵌入大型系统的计算机组成，计算机工作还需要附加电路如电源、时钟发生器和复位电路，还需要转换器（将能量从一种型式转换为另一种型式）将微处理器和外部世界相连接。转换器分为两类：输入和输出。输入（传感器）包括开关、温度传感器和按钮的等器件，输出包括LED、电机和电感线圈等。
Components in a generic microcontroller-based embedded system are showed in the gray box but this is not definitive for every MCU.
典型的基于微处理器的通用嵌入式系统地组成部分表示在灰框内。
- A power supply is necessary to power the circuit.
- An oscillator is required to drive the system’s digital logic.
- A processor is required to execute program instructions.
- A reset circuit is required to ensure the processor starts correctly on power-up or when a reset is requested.
- Nonvolatile memory is required to hold the program and fixed data.
电路供电的电源必备。
驱动系统数字逻辑的振荡器必备。
执行程序指令的处理器必备。
上电或者需要复位时保证处理器正常启动的复位电路必须。
保存程序和固定数据的非易失性信息存储必须。
电源 Power Supply
A microcontroller requires electrical power to run. To ensure that the chip will operate as expected, a system should never be designed to operate too close to the absolute maximum ratings. Within the safe operating range, the clock speed at the lower voltages may be limited. Oscillators may only run at low frequencies with lower voltages. Also, transistor switching speed falls as Vsupply - �Vthreshold falls,
微处理器需要供电才能运行，为保证芯片按照预期功能动作，系统设计不可接近极限参数运行。在安全操作范围内，时钟速度在电压较低时可能受限，低电压时振荡器只能低频运行，而且晶体管开关速度随着V电源电压 - �V 阈值电压的减小而降低，因此信号通过慢速逻辑电路需要较长的时钟周期。
For example, the RL78G14’s main clock system oscillator can run at up to 4.0 MHz with a 1.6 to 1.8V supply, up to 8 MHz with a supply above 1.8 V but below 2.7 V, and up to 20 MHz with a supply above 2.7 V. MCUs typically have built-in circuitry for dividing or multiplying the oscillator frequency to derive a different final operating frequency for the internal logic.
MCU通常具有内置电路，来对振荡器频率进行分频或倍频，产生内部逻辑所需不同最终工作频率。
时钟信号发生 Clock Signal Generation
Microprocessors are synchronous circuits that require a clock to work. This clock allows data to be pushed through the stages of the instruction pipeline and helps the microprocessor coordinate tasks. When selecting a clock generator, the microcontroller datasheet must be used. This datasheet gives the values of the different clocks that a particular microprocessor can accept.
微处理器是需要时钟工作的同步电路。 此时钟允许数据被推送通过指令流水线的各级，并帮助微处理器协调任务。 选择时钟发生器时，必须使用微控制器数据手册。 本数据手册给出了特定微处理器可以接受的不同时钟的值。
