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1、英语翻译 Microcontroller reset is to make the CPU and other system features are in a defined initial state, and from this state to work, reset PC = 0000H, the microcontroller from the first - a unit to take command. Whether it is connected to the microcontroller when the power is just the beginning, or
2、after power failure or failure to be reset. MCU reset conditions are: the RST pin must be coupled with continued two machine cycles (ie 24 oscillations) is high. Clock frequency in this article 12MHz, each machine cycle is 1s, then the only 2s time high above, appears in the RST pin high after the i
3、mplementation of the second machine cycle reset. Reset circuit constituted by the capacitor series resistance, combined with the map, the capacitor voltage can not be mutatedin nature, can know when the system is a power, RST will be a foot high, and that the duration of this high by the circuit The
4、 RC values to decide. Appropriate combination of RC values can ensure a reliable reset. The circuit in addition to a power-on reset functions, to reset, just press the RESET button, then power through resistance, voltage, reset in the RESET high end. Clock circuit main task is to provide a working f
5、requency. Internal microcontroller used to form a high-gain inverting amplifier oscillator, the amplifier input and output are XTAL1 and XTAL2, XTAL1 and XTAL2 on the external clock source can constitute a clock circuit. Both internal and external clock generation mode. This design uses the internal
6、 clock generation means. Circuit connection shown in Figure 3.2, both ends of the jumper XTAL1 and XTAL2 crystal resonator (oscillator frequency 12MHZ), and internal self-excited oscillator inverter constituted. The issue of pulse timing control directly into the on-chip components. In addition, the
7、 capacitance of the frequency tuning role, as an external crystal oscillator, capacitor selection 20pF, practical application, and capacitor resonator near as possible to install in the SCM to reduce the parasitic capacitance, the oscillator stable and reliable work. Ultrasonic transmitting circuit
8、includes ultrasonic generator circuit and the ultrasonic transmitter control circuit of two parts, ultrasound probes (also known as ultrasonic transducer) use CSB40T. 40KHz is the use of ultrasonic oscillation drive circuit 555 produce ultrasonic probe. 555 constituted by the multivibrator timer (sh
9、own in Figure 3.3). Power, the power by charging the capacitor and, when 1 / 3, the oscillator output = 1, the discharge end. When the charge to 2 / 3, the oscillator output flip to 0, then discharge tube turns on, the discharge end (DIS) grounded, capacitor C discharges through the ground, so that
10、decline. Present down to 1 / 3, the oscillator output and turn into 1, discharge and cut-off time, so that the discharge end (DIS) is not grounded, power, and again by charging the capacitor, and also allows from 1 / 3 up to 2 / 3, flip-flop flip took place, again and again to be a continuous change
11、 in the output of the oscillator pulse. Pulse width of 0.7, determined by the capacitor discharge time; = 0.7 (+), determined by the capacitor charging time, pulse period T +. The oscillation frequency calculated as f = 1.43 / (+2). Ultrasonic transmitter circuit (shown in Figure 3.4) will be design
12、ed to be adjustable resistance for the purpose of adjusting the signal frequency, so that the transducer 40kHz with the natural frequency of the same. Formed using 555 timer multivibrator duty cycle can regulate a wide range, and circuit design is simple, small footprint. 555 timer is reset terminal
13、 4 feet, use it to control the emission of ultrasonic pulses. When the 4 pin is low, there is oscillation pulse output 555; is high, the timer 555 is cleared, there is no output. Thus, the 4 foot connecting with the MCU control signals can control the transmitter. To ensure that 555 has sufficient d
14、rive capability, should adopt the +12 V supply that is = 12V. 4 feet for the ultrasonic emission control signal input from the microcontroller control. Acoustic receivers includes receiving ultrasound probe, the signal amplification circuit and waveform converting circuit of three parts. Ultrasonic
15、probe must be used with the transmitter probe corresponding models, the key is the frequency to be consistent, the design uses CSB40R, otherwise it will not produce resonance effects due to reception, if not impossible to receive. As the probe transformed by the very weak sine wave signal, it must b
16、e amplified by the amplifier. Sine wave signal microcontroller can not directly be received waveform must change. In accordance with the principles discussed above, the microcontroller needs only the first echo of the moment. Receiving circuit shown in Figure 3.6. Ultrasonic wave propagation in the air, its energy is proportional to the distance attenuation, namely, the closer the signal is stronger, the greater the distance the weaker
