【文章內(nèi)容簡介】 d. The lock bits cannot be verified directly. Verification of the lock bits is achieved by observing that their features are enabled. Chip Erase: The entire PEROM array (2 Kbytes) and the two Lock Bits are erased electrically by using the proper bination of control signals and by holding low for 10 ms. The code array is written with all 1s in the Chip Erase operation and must be executed before any nonblank memory byte can be reprogrammed. Reading the Signature Bytes: The signature bytes are read by the same procedure as a normal verification of locations 000H, 001H, and 002H, except that and must be pulled to a logic low. The values returned are as follows. 8 (000H) = 1EH indicates manufactured by Atmel (001H) = 21H indicates 89C2051 Programming Interface Every code byte in the Flash array can be written and the entire array can be erased by using the appropriate bination of control signals. The write operation cycle is selftimed and once initiated, will automatically time itself to pletion. All major programming vendors offer worldwide support for the Atmel microcontroller series. Please contact your local programming vendor for the appropriate software revision. 9 Ultrasonic ranging system design Publication title: Sensor Review. Bradford: 1993. Vol. ABSTRACT： Ultrasonic ranging technology has wide using worth in many fields，such as the industrial locale， vehicle navigation and sonar engineering． Now it has been used in level measurement ， selfguided autonomous vehicles, fieldwork robots automotive navigation， air and underwater target detection， identification， location and so on． So there is an important practicing meaning to learn the ranging theory and ways deeply. To improve the precision of the ultrasonic ranging system in hand， satisfy the request of the engineering personnel for the ranging precision， the bound and the usage，a portable ultrasonic ranging system based on the single chip processor was developed． Keywords： Ultrasound r， Ranging System， Single Chip Processor With the development of science and technology, the improvement of people39。s standard of living, speeding up the development and construction of the city. urban drainage system have greatly developed their situation is constantly improving. However, due to historical reasons many unpredictable factors in the synthesis of her time, the city drainage system. In particular drainage system often lags behind urban construction. Therefore, there are often good building excavation has been building facilities to upgrade the drainage system phenomenon. It brought to the city sewage, and it is clear to the city sewage and drainage culvert in the sewage treatment system. fort is very important to people39。s lives. Mobile robots designed to clear the drainage culvert and the automatic control system Free sewage culvert clear guarantee robot, the robot is designed to clear the culvert sewage to the core. Control System is the core ponent of the development of ultrasonic range finder. Therefore, it is very important to design a good ultrasonic range finder. 2. A principle of ultrasonic distance measurement The principle of piezoelectric ultrasonic generator 10 Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown, it has two piezoelectric chip and a resonance plate. When it39。s two plus pulse signal, the frequency equal to the intrinsic piezoelectric oscillation frequency chip, the chip will happen piezoelectric resonance, and promote the development of plate vibration resonance, ultrasound is generated. Conversely, if the two are not interelectrode voltage, when the board received ultrasonic resonance, it will be for vibration suppression of piezoelectric chip, the mechanical energy is converted to electrical signals, then it bees the ultrasonic receiver. The traditional way to determine the moment of the echo39。s arrival is based on thresholding the received signal with a fixed reference. The threshold is chosen well above the noise level, whereas the moment of arrival of an echo is defined as the first moment the echo signal surpasses that threshold. The intensity of an echo reflecting from an object strongly depends on the object39。s nature, size and distance from the sensor. Further, the time interval from the echo39。s starting point to the moment when it surpasses the threshold changes with the intensity of the echo. As a consequence, a considerable error may occur Even two echoes with different intensities arriving exactly at the same time will surpass the threshold at different moments. The stronger one will surpass the threshold earlier than the weaker, so it will be considered as belonging to a nearer object. principle of ultrasonic distance measurement Ultrasonic transmitter in a direction to launch ultrasound, in the moment to launch the beginning of time at the same time, the spread of ultrasound in the air, obstacles on his way to return immediately, the ultrasonic reflected wave received by the receiver immediately stop the clock. Ultrasound in the air as the propagation velocity of 340m / s, according to the timer records the time t, we can calculate the distance between the launch distance barrier (s), that is: s = 340t / 2 Ranging System for the Second Circuit Design System is characterized by singlechip microputer to control the use of ultrasonic transmitter and ultrasonic receiver since the launch from time to time, singlechip selection of 8751, economictouse, and the chip has 4K of ROM, to facilitate programming. Circuit schematic diagram shown in Figure 2. 11 Figure 1 circuit principle diagram 40 kHz ultrasonic pulse generated with the launch Ranging system using the ultrasonic sensor of piezoelectric ceramic sensors UCM40, its