Brief highlights the design of industrial instrumentation programmable dual-channel D / A converter TLC5618 the way to achieve channel D / A converter , while the other channel with its With a simple software program to an external circuit through successive comparison method To realize A / D conversion function of application examples Key words digital-analog (D / A) converter module (A / D) converter , TLC5618 Introduction With the continuous improvement of industrial automation , instrumentation used in industry increasingly intelligent, multifunction , small size, most of the hardware circuit design using single chip microprocessor core , which together with the external circuit. As part of the instrument need to live analog signal into digital signal single chip to handle input , then SCM obtained by the data processing digital signals into analog signal output , therefore , these instruments need to have both the hardware circuit design modules ( A / D) converter and D (D / A) conversion of two functions . At the same time need to D / A and A / D conversion instrument , you can use an A / D converter and a D / A converter is realized for A / D and D / A conversion , but because of A / D and D / A converter chip, the higher the price , the higher the cost of instrumentation . The author in the design of an industrial instrument programmable dual-channel D / A converter TLC5618 to achieve a channel D / A converter , while the other channel with its software programming to more ways to achieve successive A / D functions . Good practical application , the application method has the following characteristics : ? save an A / D converter, reduces the instrument cost . ? TLC5618 small (8 -pin mini D package ), to facilitate small-scale design, reduced PCB area . ? TLC5618 a 3 -wire serial data input , taking up CPU, I / O port line of small , overlapping hardware simple little devices , software programming convenience . ? For standard signal 1 ~ 5V signal TLC5618 can reach a resolution of at least 1.3mV, can satisfy the accuracy requirements of industrial process control . ? through software programming with successive comparison method to achieve A / D conversion set-up time is about 400µs. TLC5618 Application The following describes the specific use of a programmable dual-channel D / A converter TLC5618 to achieve a channel D / A converter , while the other channel with its software programming to more ways to achieve successive A / D conversion function of the practical application of methods . The hardware design shown in Figure 1 TLC5618 is of a buffered reference input (high impedance ) of the dual 12-bit voltage output digital -analog converter (DAC), 8 -pin mini D package , need to +5 V single power supply , the output voltage range of the two reference voltage Times , therefore , the circuit design uses a 1.2V reference voltage (eg LM385). By CMOS -compatible 3-wire serial bus microcontroller, digital control of the TLC5618 device to receive input for the program 's 16-bit words generate output . 16-bit input words of the high four bits for the program control , by programming control bits set , you can have three different output modes , low- 12 to be converted to digital . Data from the serial data input DIN from high to low by the order input , single chip serial communication can work in the operation mode 0, serial port for synchronous shift register with or use other I / O serial port simulation The realization of digital control . It is worth noting here the work of the MCU operating mode 0, when the serial port to send or receive 8 -bit data , and low in front, with the TLC5618 data reception timing contrary . Therefore, the level of SCM should first data bit after the exchange of data to send . Figure 1 is a TLC5618 realize A / D conversion and D / A conversion application circuit Click to enlarge 1.D / A function to achieve This feature is only occupied by TLC5618 's OUTB output channel , if the specified time for establishing 3µs, the former four programming control bits should be 00xx. 4 -bit pre- programmed control and are converted to digital form 12-bit 8-bit + high- low 8-bit = 16-bit input word , from the serial data input DIN from high to low according to the order input voltage from the conversion result TLC5618 's OUTB output . The circuit through the VI conversion circuit ( see Figure 1) to achieve voltage to current converter . Cheung described here no longer . 2.A / D function to achieve In this circuit is not alone A / D converter , A / D conversion by dual D / A converter TLC5618 another output channel OUTA, through an amplification circuit and compare circuit , and through software programming with successive Comparative law to achieve. That is, dual-channel D / A converter TLC5618 serial data input DIN successive input bit sequence according to the specified 12-bit digital (such as x800h), and enter the number each time the amount of D / A conversion results with the actual input Analog voltage comparison, compare the results to determine for each designated position should be " 0 "or "1" , when the last one is confirmed, this bit is specified by the ultimate digital A / D conversion results . Specific works as follows: Each A / D conversion process , the first four bits have been programmed for the 10xx. Before and after the 4-bit programming bit 12-bit digital conversion to high 8 + 8 = 16-bit low- input word . Each A / D converter before the specified 12-bit digital input (not including the four programming bits) of the highest bit is " 1 " for imported TLC5618 D / A converter , D / A conversion results from the OUTA output , after a one Stage amplifier, by comparing the actual input of the analog circuit and voltage comparison . If the conversion result of analog input voltage is greater than the voltage , the transistor base is extremely high T1 , T1 turn , P0.2 was down to low ; otherwise the conversion results less than the input voltage analog voltage , the transistor T1 -based Extremely low , T1 end , P0.2 is pull as high . MCU by detecting the state of P0.2 , if P0.2 is high , then the reservation -based "1 "; if P0.2 is low , will be based "1 "to" 0 . " This 12-digit volume of 1 was determined, and then specify the next "1" , through the D / A conversion, amplification , comparison, and to detect the state of P0.2 , the position has been determined . And so on , until all 12-bit digital to be determined, the 12-bit digital representation of the D / A conversion results will be closest to the input analog voltage , it actually is the A / D conversion results. Note that the detection MCU I / O comparison state, should be added to the time delay of about 10µs . In addition, the circuit only has an analog input signal , For more than one analog input signal , analog switches can not add , only add more circuitry , multiple analog input signals can be with the D / A Converter After an amplifier output signal are compared by corresponding A / D conversion routines to achieve A / D conversion . Conclusion Increasingly in the industrial instrument to function , intelligence, small development today, dual-channel D / A converter TLC5618 performance of its advantages more and more popular. Full application of the circuit performance characteristics of the TLC5618 , which greatly reduces hardware costs , improved product performance and low cost . I believe that programmable dual-channel D / A converter TLC5618 is a widely used product is worth .