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ADC0803-1CN データシート(PDF) 8 Page - NXP Semiconductors |
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ADC0803-1CN データシート(HTML) 8 Page - NXP Semiconductors |
8 / 18 page Philips Semiconductors Product data ADC0803/0804 CMOS 8-bit A/D converters 2002 Oct 17 8 APPLICATIONS Microprocessor Interfacing This family of A/D converters was designed for easy microprocessor interfacing. These converters can be memory mapped with appropriate memory address decoding for CS (read) input. The active-Low write pulse from the processor is then connected to the WR input of the A/D converter, while the processor active-Low read pulse is fed to the converter RD input to read the converted data. If the clock signal is derived from the microprocessor system clock, the designer/programmer should be sure that there is no attempt to read the converter until 74 converter clock pulses after the start pulse goes high. Alternatively, the INTR pin may be used to interrupt the processor to cause reading of the converted data. Of course, the converter can be connected and addressed as a peripheral (in I/O space), as shown in Figure 12. A bus driver should be used as a buffer to the A/D output in large microprocessor systems where the data leaves the PC board and/or must drive capacitive loads in excess of 100 pF. See Figure 14. Interfacing the SCN8048 microcomputer family is pretty simple, as shown in Figure 13. Since the SCN8048 family has 24 I/O lines, one of these (shown here as bit 0 or port 1) can be used as the chip select signal to the converter, eliminating the need for an address decoder. The RD and WR signals are generated by reading from and writing to a dummy address. Digitizing a Transducer Interface Output Circuit Description Figure 15 shows an example of digitizing transducer interface output voltage. In this case, the transducer interface is the NE5521, an LVDT (Linear Variable Differential Transformer) Signal Conditioner. The diode at the A/D input is used to insure that the input to the A/D does not go excessively beyond the supply voltage of the A/D. See the NE5521 data sheet for a complete description of the operation of that part. Circuit Adjustment To adjust the full scale and zero scale of the A/D, determine the range of voltages that the transducer interface output will take on. Set the LVDT core for null and set the Zero Scale Scale Adjust Potentiometer for a digital output from the A/D of 1000 000. Set the LVDT core for maximum voltage from the interface and set the Full Scale Adjust potentiometer so the A/D output is just barely 1111 1111. A Digital Thermostat Circuit Description The schematic of a Digital Thermostat is shown in Figure 16. The A/D digitizes the output of the LM35, a temperature transducer IC with an output of 10 mV per °C. With VREF/2 set for 2.56 V, this 10 mV corresponds to 1/2 LSB and the circuit resolution is 2 °C. Reducing VREF/2 to 1.28 yields a resolution of 1 °C. Of course, the lower VREF/2 is, the more sensitive the A/D will be to noise. The desired temperature is set by holding either of the set buttons closed. The SCC80C451 programming could cause the desired (set) temperature to be displayed while either button is depressed and for a short time after it is released. At other times the ambient temperature could be displayed. The set temperature is stored in an SCN8051 internal register. The A/D conversion is started by writing anything at all to the A/D with port pin P10 set high. The desired temperature is compared with the digitized actual temperature, and the heater is turned on or off by clearing setting port pin P12. If desired, another port pin could be used to turn on or off an air conditioner. The display drivers are NE587s if common anode LED displays are used. Of course, it is possible to interface to LCD displays as well. |
同様の部品番号 - ADC0803-1CN |
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同様の説明 - ADC0803-1CN |
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