双线ADC，SPI读取

Question

我使用Arduino UNO（Atmega328）和12位ADC组件（AD7893ANZ-10），数据表可在https://www.analog.com/media/en/technical-documentation/data-sheets/AD7893.pdf

问题：我已经尝试了几个不同的代码，但读取值总是错误的，即使ADC的SDATA引脚未连接到Arduino的MISO引脚，我也会得到相同的值（参见图1）。我在proteus中模拟了它（参见图2），并在proteus中使用了虚拟串行监视器。Arduino的MOSI和SS引脚未连接，但我将代码中的SS引脚设置为低和高，以满足库要求。有关ADC定时的更多信息将作为注释添加到下面的代码中。或在数据表中提供。如果你看一下，我会非常感激的，因为我不知道我做错了什么。

PS:ADC只需连接引脚即可与SPI:1.SDATA（slaveout）和2.SCLK进行通信。ADC上的引脚CONVST用于启动转换。

#include <SPI.h>
   //source of code https://www.gammon.com.au/spi
void setup() {

  Serial.begin (115200);
  pinMode(7, OUTPUT);   // this pin is connected to convst on adc to initiate conversion


  // Put SCK, MOSI, SS pins into output mode (introductions from source)
  // also put SCK, MOSI into LOW state, and SS into HIGH state.
  // Then put SPI hardware into Master mode and turn SPI on
  pinMode(SCK, OUTPUT);
  pinMode(MOSI, OUTPUT);
  pinMode(SS, OUTPUT);
  digitalWrite(SS, HIGH);
  digitalWrite(SCK, LOW); 
  digitalWrite(MOSI, LOW);
  SPCR = (1<<MSTR);
  SPI.begin ();
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE1)); // set the clk frequency; take the MSB first;
                                                                    //mode1 for CPOL=0 and CPHA=1 according to datasheet p.9 "CPOL bit set to a logic zero and its CPHA bit set to a logic one."
}


int transferAndWait (const byte what)  //methode to read data
{ 
  int a = SPI.transfer(what);    //send zero(MOSI not connected)and  read the first 8 bits and save
  Serial.println (a);            // show the value, in serial monitor -1
  a =(a << 8);                   //shift the saved first 8 bits to left
  Serial.println (a);            // show the value, in serial monitor 255
  a = a | SPI.transfer(what);     //read and save the last  8 bits
  Serial.println (a);             // show the value, in serial monitor -256
  delayMicroseconds (10);
  return a;
}


void loop() {
  int k;
  digitalWrite(7, HIGH);      //set pin high to initiate the conversion
  delayMicroseconds(9);       //the conversion time needed, actually 6 mikroseconds

  digitalWrite(SS, LOW);    // enable Slave Select  to get the library working
  k = transferAndWait (0);  //call the method
  delayMicroseconds(1);
  digitalWrite(7, LOW);     
  digitalWrite(SS, HIGH);   //disable chip select
  delay(2000);              //delay just to keep the overview on serial monitor
  Serial.println (k);       // show the value, in serial monitor -1
}

Answer 1

首先，返回变量应该是无符号整数，而不是有符号整数。此外，CONVST应该只在短时间内低，因为转换是在之后开始的。请参见定时顺序。