STM32模拟SPI协议获取24位模数转换（24bit ADC）芯片AD7791电压采样数据

STM32模拟SPI协议获取24位模数转换（24bit ADC）芯片AD7791电压采样数据

STM32大部分芯片只有12位的ADC采样性能，如果要实现更高精度的模数转换如24位ADC采样，则需要连接外部ADC实现。AD7791是亚德诺(ADI)半导体一款用于低功耗、24位Σ-Δ型模数转换器(ADC) ,适合低频测量应用，提供50 Hz/60 Hz同步抑制。

这里介绍基于AD7791的24位ADC采样实现。

AD7791控制协议

AD7791的管脚如下所示：

AD7791可以工作在2.5V~5.25V供电范围（VDD），而用于模数转换的参考电压可以通过引脚REFIN(+)和REFIN(–)单独设置，从而可以针对特定电压范围更高精度的采样。如果REFIN(+) - REFIN(–) = 1V， 则对应24位采样分辨率率为1/(2^24)=0.00000006V。当然要使得这个级别的电压分辨率有效，对电路噪声的控制要求也很高。
AIN(+)和AIN(-)用于连接输入信号，通过芯片内部寄存器配置，有两种转换模式，即AIN(+)相对AIN(-)是单边电压或双边电压。单边电压模式，采样值0x000000对应AIN(+)-AIN(-)=0，采样值0xFFFFFF对应AIN(+)-AIN(-)=REFIN(+) - REFIN(–) 。双边电压模式，采样值0x000000对应AIN(+)-AIN(-)=-(REFIN(+) - REFIN(–))，采样值0x800000对应AIN(+)-AIN(-)=0，采样值0xFFFFFF对应AIN(+)-AIN(-)=REFIN(+) - REFIN(–) 。
AD7791通过SPI总线进行访问控制，其中数据输出管脚DOUT也是转换完成可读取指示信号/RDY, 访问协议操作主要逻辑如下：

1. 向通讯寄存器发送指令，设置采样的通道和读操作模式（单次或连续），并且设置下一次访问是对哪个寄存器进行操作，以及进行的是读还是写；
2. 写模式寄存器，设置采用单次转换还是连续转换模式，单边还是双边转换模式，以及是否buffered模式（buffered模式对应信号接收管脚端接收阻抗高阻模式），以及buffered模式是否在输入端引用100ns电流源;
3. 在配置模式寄存器后，可以再向通讯寄存器发送指令指示后续读取数据寄存器，然后按照24位格式读取采样到的ADC值;
4. 芯片支持对供电电压的采样识别，原理为供电电压内部LDO降压到1.17V作为VDD采样电路的参考供电，而VDD本身分压到1/5接到ADC采样端。所以供电电压识别为(VDD采样值/16777216)1.175 V.
5. 可配置滤波寄存器以控制采样转换输出频率，影响到噪声抑制级别；
6. 可以读取状态寄存器获得一些状态信息。

STM32工程配置

这里以STM32F103C6T6及STM32CUBEIDE开发工具为例，介绍AD7791的24位ADC采样实现。

首先建立基本工程并配置时钟：



配置一个串口如UART2作为通讯打印输出口

再选择4根管脚作为模拟协议用的GPIO, 这里用PA15作为CS，PB3作为CLK，PB4作为MISO， PB5作为MOSI，各管脚上外部电阻上拉到AD7791的供电电压，STM32的管脚配置为Open-drain模式，从而可以兼容不同供电电压的AD7791访问连接, 因此STM32的GPIO也都选择为具有FT(5V耐压)能力的管脚。

保存并生成基本工程代码：

STM32工程代码

AD7791的ADC数据读取有5种模式：

1. 单次转换单次单读
2. 单次转换多次单读（读到同样的数据）
3. 连续转换单次单读
4. 连续转换多次单读
5. 连续抓换多次连读
   其中单读和连续的区别是，单读的每次读取前要发送一次写操作，连续的所有读取前只发送一次写操作。这里的工程代码对5种模式都做了函数实现。

代码采用的微秒级延时函数实现，参考： STM32 HAL us delay（微秒延时）的指令延时实现方式及优化
代码用到串口打印printf函数的重载及采用的浮点转换函数，参考： STM32 UART串口printf函数应用及浮点打印代码空间节省 (HAL)

完整的main.c工程代码如下：

/* USER CODE BEGIN Header */
/********************************************************************************* @file           : main.c* @brief          : Main program body******************************************************************************* @attention** Copyright (c) 2022 STMicroelectronics.* All rights reserved.** This software is licensed under terms that can be found in the LICENSE file* in the root directory of this software component.* If no LICENSE file comes with this software, it is provided AS-IS.********************************************************************************/
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "usart.h"
/* USER CODE END Includes *//* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD *//* USER CODE END PTD *//* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
__IO float usDelayBase;
void PY_usDelayTest(void)
{__IO uint32_t firstms, secondms;__IO uint32_t counter = 0;firstms = HAL_GetTick()+1;secondms = firstms+1;while(uwTick!=firstms) ;while(uwTick!=secondms) counter++;usDelayBase = ((float)counter)/1000;
}void PY_Delay_us_t(uint32_t Delay)
{__IO uint32_t delayReg;__IO uint32_t usNum = (uint32_t)(Delay*usDelayBase);delayReg = 0;while(delayReg!=usNum) delayReg++;
}void PY_usDelayOptimize(void)
{__IO uint32_t firstms, secondms;__IO float coe = 1.0;firstms = HAL_GetTick();PY_Delay_us_t(1000000) ;secondms = HAL_GetTick();coe = ((float)1000)/(secondms-firstms);usDelayBase = coe*usDelayBase;
}void PY_Delay_us(uint32_t Delay)
{__IO uint32_t delayReg;__IO uint32_t msNum = Delay/1000;__IO uint32_t usNum = (uint32_t)((Delay%1000)*usDelayBase);if(msNum>0) HAL_Delay(msNum);delayReg = 0;while(delayReg!=usNum) delayReg++;
}/*
*Convert float to string type
*Written by Pegasus Yu in 2022
*stra: string address as mychar from char mychar[];
*float: float input like 12.345
*flen: fraction length as 3 for 12.345
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
void py_f2s4printf(char * stra, float x, uint8_t flen)
{uint32_t base;int64_t dn;char mc[32];base = pow(10,flen);dn = x*base;sprintf(stra, "%d.", (int)(dn/base));dn = abs(dn);if(dn%base==0){for(uint8_t j=1;j<=flen;j++){stra = strcat(stra, "0");}return;}else{if(flen==1){sprintf(mc, "%d", (int)(dn%base));stra = strcat(stra, mc);return;}for(uint8_t j=1;j<flen;j++){if((dn%base)<pow(10,j)){for(uint8_t k=1;k<=(flen-j);k++){stra = strcat(stra, "0");}sprintf(mc, "%d", (int)(dn%base));stra = strcat(stra, mc);return;}}sprintf(mc, "%d", (int)(dn%base));stra = strcat(stra, mc);return;}
}
/* USER CODE END PD *//* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
#define   AD7791_CS_LOW      HAL_GPIO_WritePin(GPIOA, GPIO_PIN_15, GPIO_PIN_RESET)
#define   AD7791_CS_HIGH     HAL_GPIO_WritePin(GPIOA, GPIO_PIN_15, GPIO_PIN_SET)
#define   AD7791_CLK_LOW     HAL_GPIO_WritePin(GPIOB, GPIO_PIN_3, GPIO_PIN_RESET)
#define   AD7791_CLK_HIGH    HAL_GPIO_WritePin(GPIOB, GPIO_PIN_3, GPIO_PIN_SET)
#define   AD7791_DIN_LOW     HAL_GPIO_WritePin(GPIOB, GPIO_PIN_5, GPIO_PIN_RESET)
#define   AD7791_DIN_HIGH    HAL_GPIO_WritePin(GPIOB, GPIO_PIN_5, GPIO_PIN_SET)
#define   AD7791_DOUT_nRDY         HAL_GPIO_ReadPin(GPIOB, GPIO_PIN_4)void AD7791_RST(void)
{
/** The serial interface can be reset by writing a series of 1s on the DIN input. If a Logic 1 is written to the AD7791 line for at least* 32 serial clock cycles, the serial interface is reset.** The DOUT/ RDY pin operates as a Data Ready signal also, the line going low when a new data-word is available in the output register.* It is reset high when a read operation from the data register is complete.* It also goes high prior to the updating of the data register to indicate when not to read from the device to ensure that a data read is* not attempted while the register is being updated.*/AD7791_CS_HIGH;AD7791_DIN_HIGH;AD7791_CLK_HIGH;AD7791_CS_LOW;PY_Delay_us_t(1);for(uint8_t i=0;i<32;i++){AD7791_CLK_LOW;PY_Delay_us_t(1);AD7791_CLK_HIGH;PY_Delay_us_t(1);}AD7791_DIN_LOW;AD7791_CS_HIGH;
}/** write access to any of the other registers on the part begins with a write operation to the communications register followed by a* write to the selected register.* A read operation from any other register (except when continuous read mode is selected) starts* with a write to the communications register followed by a read operation from the selected register.*/void AD7791_WR_1BYTE(uint8_t cmd) //write 8-bit data
{for(uint8_t i=0; i<8; i++){AD7791_CLK_LOW;if ((cmd<<i)&0x80) AD7791_DIN_HIGH;else AD7791_DIN_LOW;PY_Delay_us_t(1);AD7791_CLK_HIGH;PY_Delay_us_t(1);}}uint32_t AD7791_RD_3BYTE(void) //read 24-bit data
{uint8_t rbit = 0;uint32_t rdata = 0;for(uint8_t i=1; i<=24; i++){PY_Delay_us_t(1);AD7791_CLK_LOW;PY_Delay_us_t(1);AD7791_CLK_HIGH;rbit = AD7791_DOUT_nRDY;if (rbit != 0) rdata |= (((uint32_t)rbit)<<(24-i));}return rdata;
}void AD7791_POWER_DOWN(void)
{AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0xc4);AD7791_CS_HIGH;
}uint8_t AD7791_READ_STATUS_REG(void)
{uint8_t rbit = 0;uint8_t rdata = 0;AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x08);AD7791_DIN_LOW;AD7791_CLK_HIGH;for(uint8_t i=1; i<=8; i++){PY_Delay_us_t(1);AD7791_CLK_LOW;PY_Delay_us_t(1);AD7791_CLK_HIGH;rbit = AD7791_DOUT_nRDY;if (rbit != 0) rdata |= ((rbit)<<(8-i));}AD7791_CS_HIGH;return rdata;
}uint8_t AD7791_SET_FILTER_REG(uint8_t data)
{/** Due to chip fault, 0 or 1 written to lowest bit of filter register will become 1. So to write 0x04 will get back-read value 0x05.* So don't write filter register if you want to keep 0x04 in filter register which will be filled 0x04 when power up.*/uint8_t mode = 0x04; //default: clock without division, 16.6Hz output rateuint8_t rbit = 0;uint8_t rdata = 0;AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x20);mode = data;AD7791_WR_1BYTE(mode);AD7791_CS_HIGH;AD7791_RST();PY_Delay_us_t(1);AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x28);AD7791_DIN_LOW;AD7791_CLK_HIGH;for(uint8_t i=1; i<=8; i++){PY_Delay_us_t(1);AD7791_CLK_LOW;PY_Delay_us_t(1);AD7791_CLK_HIGH;rbit = AD7791_DOUT_nRDY;if (rbit != 0) rdata |= ((rbit)<<(8-i));}AD7791_CS_HIGH;return rdata;}uint32_t AD7791_SAMPLE_VDD_SINGLE(void)
{
/*
* Along with converting external voltages, the analog input chan-nel can be used to monitor the voltage on the VDD pin.
* When the CH1 and CH0 bits in the communications register are set to 1,
* the voltage on the VDD pin is internally attenuated by 5 and the resultant voltage is applied to the Σ-Δ modulator using an internal 1.17 V reference for analog to digital conversion.
*/uint32_t vdd = 0;AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x17);AD7791_WR_1BYTE(0x06);while(AD7791_DOUT_nRDY) ;AD7791_WR_1BYTE(0x3f);vdd = AD7791_RD_3BYTE();AD7791_CS_HIGH;AD7791_RST();return vdd;/** voltage = (vdd/16777216)*1.17*5*/
}/* ** Mode1: single conversion mode + single read mode : get one-time 24-bit data (write operation advanced before read operation)* Mode2: single conversion mode + multi-time single read mode: get multi-time same 24-bit data (write operation advanced before every read operation)* Mode3: continuous conversion mode + single read mode: get one-time 24-bit data (write operation advanced before read operation)* Mode4: continuous conversion mode + multi-time single read mode: get multi-time individual 24-bit data (write operation advanced before every read operation)* Mode5: continuous conversion mode + continuous read mode: get multi-time individual 24-bit data (only once write operation for all read operations)*/void AD7791_Mode1_RD(uint32_t *result)
{AD7791_CLK_HIGH;AD7791_CS_LOW;//AD7791_WR_1BYTE(0x12); //used for AIN(–) – AIN(–) test onlyAD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0x86);//single conversion mode, no burn-out current, uni-polar and bufferedwhile(AD7791_DOUT_nRDY) ;AD7791_WR_1BYTE(0x38);//single read(*result) =  AD7791_RD_3BYTE();AD7791_CS_HIGH;AD7791_RST();
}void AD7791_Mode2_RD(uint32_t *result, uint32_t times)
{AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0x86);//single conversion mode, no burn-out current, uni-polar and bufferedwhile(AD7791_DOUT_nRDY) ;for(uint32_t i=0; i<times; i++){AD7791_WR_1BYTE(0x38);//single readresult[i] = AD7791_RD_3BYTE();PY_Delay_us_t(1);}AD7791_CS_HIGH;AD7791_RST();
}void AD7791_Mode3_RD(uint32_t *result)
{AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0x06);//continuous conversion mode, no burn-out current, uni-polar and bufferedwhile(AD7791_DOUT_nRDY) ;AD7791_WR_1BYTE(0x38);//single read(*result) =  AD7791_RD_3BYTE();AD7791_CS_HIGH;AD7791_RST();
}void AD7791_Mode4_RD(uint32_t *result, uint32_t times)
{AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0x06);//continuous conversion mode, no burn-out current, uni-polar and bufferedfor(uint32_t i=0; i<times; i++){while(AD7791_DOUT_nRDY) ;AD7791_WR_1BYTE(0x38);//single readresult[i] =  AD7791_RD_3BYTE();PY_Delay_us_t(1);}AD7791_CS_HIGH;AD7791_RST();
}void AD7791_Mode5_RD(uint32_t *result, uint32_t times)
{AD7791_CLK_HIGH;AD7791_CS_LOW;AD7791_WR_1BYTE(0x10);AD7791_WR_1BYTE(0x06);//continuous conversion mode, no burn-out current, uni-polar and bufferedAD7791_WR_1BYTE(0x3c);//continuous readfor(uint32_t i=0; i<times; i++){while(AD7791_DOUT_nRDY) ;result[i] =  AD7791_RD_3BYTE();PY_Delay_us_t(1);}AD7791_CS_HIGH;AD7791_RST();
}
/* USER CODE END PM *//* Private variables ---------------------------------------------------------*/
UART_HandleTypeDef huart2;/* USER CODE BEGIN PV *//* USER CODE END PV *//* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USART2_UART_Init(void);
/* USER CODE BEGIN PFP *//* USER CODE END PFP *//* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 *//* USER CODE END 0 *//*** @brief  The application entry point.* @retval int*/
int main(void)
{/* USER CODE BEGIN 1 */uint32_t AData[128];float vdd;char mychar[100];/* USER CODE END 1 *//* MCU Configuration--------------------------------------------------------*//* Reset of all peripherals, Initializes the Flash interface and the Systick. */HAL_Init();/* USER CODE BEGIN Init *//* USER CODE END Init *//* Configure the system clock */SystemClock_Config();/* USER CODE BEGIN SysInit *//* USER CODE END SysInit *//* Initialize all configured peripherals */MX_GPIO_Init();MX_USART2_UART_Init();/* USER CODE BEGIN 2 */PY_usDelayTest();PY_usDelayOptimize();/* USER CODE END 2 *//* Infinite loop *//* USER CODE BEGIN WHILE */while (1){printf("Status Register Read Value=0x%02x\r\n", AD7791_READ_STATUS_REG());printf("Filter Register Set Value=0x%02x\r\n", AD7791_SET_FILTER_REG(0x05));vdd = ((float)AD7791_SAMPLE_VDD_SINGLE())*1.17*5/16777216;py_f2s4printf(mychar, vdd, 6);printf("VDD Sampling Read Value=%s V\r\n", mychar);AD7791_Mode1_RD(AData);printf("Mode 1 Signal Sampling Read Value=%d\r\n", AData[0]);AD7791_Mode2_RD(AData, 4);printf("Mode 2 Signal Sampling Read Value:\r\n%d\r\n%d\r\n%d\r\n%d\r\n", AData[0], AData[1], AData[2], AData[3]);AD7791_Mode3_RD(AData);printf("Mode 3 Signal Sampling Read Value=%d\r\n", AData[0]);AD7791_Mode4_RD(AData, 4);printf("Mode 4 Signal Sampling Read Value:\r\n%d\r\n%d\r\n%d\r\n%d\r\n", AData[0], AData[1], AData[2], AData[3]);AD7791_Mode5_RD(AData, 4);printf("Mode 5 Signal Sampling Read Value:\r\n%d\r\n%d\r\n%d\r\n%d\r\n", AData[0], AData[1], AData[2], AData[3]);PY_Delay_us_t(1000000);printf("\r\n");/* USER CODE END WHILE *//* USER CODE BEGIN 3 */}/* USER CODE END 3 */
}/*** @brief System Clock Configuration* @retval None*/
void SystemClock_Config(void)
{RCC_OscInitTypeDef RCC_OscInitStruct = {0};RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};/** Initializes the RCC Oscillators according to the specified parameters* in the RCC_OscInitTypeDef structure.*/RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;RCC_OscInitStruct.HSEState = RCC_HSE_ON;RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;RCC_OscInitStruct.HSIState = RCC_HSI_ON;RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK){Error_Handler();}/** Initializes the CPU, AHB and APB buses clocks*/RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK){Error_Handler();}
}/*** @brief USART2 Initialization Function* @param None* @retval None*/
static void MX_USART2_UART_Init(void)
{/* USER CODE BEGIN USART2_Init 0 *//* USER CODE END USART2_Init 0 *//* USER CODE BEGIN USART2_Init 1 *//* USER CODE END USART2_Init 1 */huart2.Instance = USART2;huart2.Init.BaudRate = 115200;huart2.Init.WordLength = UART_WORDLENGTH_8B;huart2.Init.StopBits = UART_STOPBITS_1;huart2.Init.Parity = UART_PARITY_NONE;huart2.Init.Mode = UART_MODE_TX_RX;huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;huart2.Init.OverSampling = UART_OVERSAMPLING_16;if (HAL_UART_Init(&huart2) != HAL_OK){Error_Handler();}/* USER CODE BEGIN USART2_Init 2 *//* USER CODE END USART2_Init 2 */}/*** @brief GPIO Initialization Function* @param None* @retval None*/
static void MX_GPIO_Init(void)
{GPIO_InitTypeDef GPIO_InitStruct = {0};/* GPIO Ports Clock Enable */__HAL_RCC_GPIOD_CLK_ENABLE();__HAL_RCC_GPIOA_CLK_ENABLE();__HAL_RCC_GPIOB_CLK_ENABLE();/*Configure GPIO pin Output Level */HAL_GPIO_WritePin(GPIOA, GPIO_PIN_15, GPIO_PIN_SET);/*Configure GPIO pin Output Level */HAL_GPIO_WritePin(GPIOB, GPIO_PIN_3|GPIO_PIN_4|GPIO_PIN_5, GPIO_PIN_SET);/*Configure GPIO pin : PA15 */GPIO_InitStruct.Pin = GPIO_PIN_15;GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;GPIO_InitStruct.Pull = GPIO_NOPULL;GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);/*Configure GPIO pins : PB3 PB4 PB5 */GPIO_InitStruct.Pin = GPIO_PIN_3|GPIO_PIN_4|GPIO_PIN_5;GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_OD;GPIO_InitStruct.Pull = GPIO_NOPULL;GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_HIGH;HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);}/* USER CODE BEGIN 4 *//* USER CODE END 4 *//*** @brief  This function is executed in case of error occurrence.* @retval None*/
void Error_Handler(void)
{/* USER CODE BEGIN Error_Handler_Debug *//* User can add his own implementation to report the HAL error return state */__disable_irq();while (1){}/* USER CODE END Error_Handler_Debug */
}#ifdef  USE_FULL_ASSERT
/*** @brief  Reports the name of the source file and the source line number*         where the assert_param error has occurred.* @param  file: pointer to the source file name* @param  line: assert_param error line source number* @retval None*/
void assert_failed(uint8_t *file, uint32_t line)
{/* USER CODE BEGIN 6 *//* User can add his own implementation to report the file name and line number,ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) *//* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

STM32测试输出

串口测试输出如下：

例程下载

STM32F103C6T6模拟SPI协议读取24位模数转换（24bit ADC）芯片AD7791数据例程

–End–