Interface Design between STC89C52 and 8-bit D/A Converter DAC0832

1. DAC0832 chip - current output D/A converter

8-bit parallel input mode

Resolution 19.5mV (VREF = 5V)

Current build-up time 1μS

Input compatible with TTL level

Single power supply (+5V~+15V)

Low power consumption, 20mw

1. Pin function:

DI0~DI7: 8-bit digital signal input terminal, connected to the data bus P0 port of the microcontroller, used to receive digital quantities sent by the microcontroller to be converted into analog quantities, DI7 is the highest bit.

        : Chip select terminal, when it is low level, this chip is selected.

ILE: Data latch enable control terminal, high level is valid.

      : First level input register write enable control, low level is effective.  

         =0, ILE=1, =0, the data signal to be converted is latched into the first-level 8-bit input register.

       :Data transmission control, low level is valid.

      :DAC register write enable control terminal, low level is valid.      

                     =0, =0, the data to be converted in the input register is transferred to the 8-bit DAC register.

IOUT1: D/A converter current output 1 terminal. When the input digital quantities are all "1", IOUT1 is maximum, and when the input digital quantities are all "0", IOUT1 is minimum.

IOUT2: D/A converter current output 2, IOUT2 ​​+ IOUT1 = constant.

Rfb: External feedback signal input terminal. There is an internal feedback resistor Rfb, and an external feedback resistor can also be connected as needed.

VCC: Power input terminal, within the range of +5V to +15V.

2. Structure of DAC0832

Internal composition:

1 8-bit input latch

One 8-bit DAC register

1 8-bit D/A converter

5 control logics (2-level control)

Working process: 8-bit data is sent to the latch in parallel → enters the register under the action of the first-level control signal → enters the converter under the action of the second-level control signal → the conversion result is output by the Iout1 current.

3. Three control methods of DAC0832

Pass-through mode - Both registers are in the pass-through state

The pass-through method cannot be directly connected to the system's data bus and requires an additional latch, so it is rarely used.

Single buffer mode - one register is in pass-through state and the other is in controlled state

Double buffering mode - both registers are in controlled state

2. Interface between STC89C52 and DAC0832

1. Direct control mode---both registers are in direct state

The circuit uses I/O port wiring and direct control mode - all four control terminals are connected to low level, and ILE is connected to high level. Once the digital quantity is input, it directly enters the DAC register for D/A conversion.

2. Single buffer mode --- one of the two internal data buffers is in direct mode, and the other is in latch mode controlled by the microcontroller. In practical applications, if there is only one analog output, or if there are multiple analog outputs but synchronization of multiple outputs is not required, the single buffer mode can be used.

The polarity of the unipolar output is determined by the polarity of VREF.

In the figure, ILE is connected to +5V, IOUT2 ​​is grounded, and the output current of IOUT1 is converted by the operational amplifier to output a unipolar voltage with a range of 0 to +5V. The "8-bit DAC register" of DAC0832 works in direct-through mode. The "8-bit input register" is in a controlled state and is controlled by P2.7.

When the microcontroller executes the following instruction, a low level can be generated on and , allowing DAC0832 to receive the digital value sent by STC89C52.

MOV DPTR,#7FFFH

MOV    A,#data

MOVX @DPTR,A

[Example] DAC0832 is used as a waveform generator. Write a program to generate triangular waves and rectangular waves.

Triangle wave

#include

#define DAC0832 XBYTE[0x7fff] //Set the access address of DAC0832

unsigned char num;

void main() {

  while(1){

    for (num=0;num<0xff;num++) // rising segment waveform

  DAC0832=whether;

    for (num=0xff; num > 0 ; num--) //Descending waveform

DAC0832=num; //DAC0832 conversion output

  }

}

Rectangular wave

#include

#define DAC0832 XBYTE[0x7fff] //Set the access address of DAC0832

unsigned int  i;

void main() {

  while (1) {

     for(i=0;i<10000;i++) //set the digital value corresponding to the upper limit level, delay

DAC0832=255;

     for(i=0;i<20000;i++) //set the digital value corresponding to the lower limit level, delay

      DAC0832=0;

}

}

3. Double buffering mode: both registers are in controlled state separately.

For systems that require synchronous conversion and output of multiple D/A converters, a dual-buffer synchronization method should be used. When DAC0832 works in dual-buffer mode, the input latching and D/A conversion of digital quantities are completed in two steps. First, the CPU's data bus inputs the digital quantities to be converted to each D/A converter in a time-sharing manner and latches them in their respective input latches. Then the CPU sends a control signal to all D/A converters, so that the data in the input latches of each D/A converter is entered into the DAC register to achieve synchronous conversion and output.

In the case of multi-channel D/A conversion output, in addition to the above method, multi-channel DAC chips can also be used. This DAC chip has two or more identical DACs in the same package, and they can work independently. For example, AD7528 is a dual-channel 8-bit DAC chip that can output two analog quantities at the same time; AD7526 is a quad-channel 8-bit DAC chip that can output four analog quantities at the same time.

[Example] According to the figure below, two-way D/A synchronous output is realized to generate upstream and downstream sawtooth waves.

#include

#define DAC1 XBYTE[0xdfff] //Set the access address of 1#DAC0832 input latch

#define DAC2 XBYTE[0xbfff] //Set the access address of 2#DAC0832 input latch

#define DAOUT XBYTE[0x7fff] // two DAC0832 DAC register access addresses

void main (void){

     unsigned char num; //Data to be converted

     while(1){

for(num =0; num <=255; num++){

DAC1 = num; // Upper sawtooth is sent to 1#DAC

DAC2 = 255-num; //Send the lower sawtooth to DAC#2

        DAOUT = num; //Two channels of D/A conversion output simultaneously

}

     }

}

3. Bipolar voltage output

           In situations where bipolar voltage output is required, the wiring can be done according to Figure 11-14. In the figure, the digital value of DAC0832 is sent by the microcontroller. A1 and A2 are both operational amplifiers, which are fed back to the input terminal of operational amplifier A2 through a 2R resistor. Point G is the virtual ground. The equations listed by Kirchhoff's law can be solved to get