STM32 SPI Library for AD5235 Digital Potentiometer

STM32 SPI Library for AD5235 Digital Potentiometer

Please read Liability Disclaimer and License Agreement CAREFULLY

AD5235 is a Dual 1024-Position Digital Potentiometer with Nonvolatile Memory that has the following features:

- Dual-channel, 1024-position resolution
- 25 kΩ, 250 kΩ nominal resistance
- Maximum ±8% nominal resistor tolerance error
- Low temperature coefficient: 35 ppm/°C
- 2.7 V to 5 V single supply or ±2.5 V dual supply
- SPI-compatible serial interface
- Nonvolatile memory stores wiper settings
- Power-on refreshed with EEMEM settings
- Permanent memory write protection
- Resistance tolerance stored in EEMEM

Please read AD5235 datasheet first.

This library is using SPI2 on a STM32 microcontroller, for a better understanding read this article DSLR Remote Control F7

AD5235.h

 

#ifndef __AD5235_H
#define __AD5235_H

#ifdef __cplusplus
extern "C" {
    #endif
        #include "spi.h"
        #include "myDelay.h"    
        #define SEND_LIMIT 3
        #define CMD_NOP    0x00 //0- Do nothing
        //Control and Error Registers
        #define EEMEM2RDAC        0x10 //1 - Restore EEMEM (A0) contents to RDAC (A0) register. See Table 16.
        #define RDAC2EEMEM        0x20 //2 - Store wiper setting. Store RDAC (A0) setting to EEMEM (A0). See Table 15. - Use a delay of 50ms!!!
        #define EEMEM_store        0x30 //3 - Store contents of Serial Register Data Byte 0 and Serial Register Data Bytes 1 (total 16 bits) to EEMEM (ADDR). See Table 18.- Use a delay of 50ms!!!/RDAC1 is 0, RDAC2 is 1, User1 is 2....User13 is 14
        #define Down6Db            0x40 //4 - Decrement by 6 dB. Right-shift contents of RDAC (A0) register, stop at all 0s.
        #define DownAll6Db        0x50 //5 - Decrement all by 6 dB. Right-shift contents of all RDAC registers, stop at all 0s.
        #define Down1            0x60 //6 - Decrement contents of RDAC (A0) by 1, stop at all 0s.
        #define Down1All        0x70 //7 - Decrement contents of all RDAC registers by 1, stop at all 0s.
        #define AllRDAC         0x80 //8 - Reset. Refresh all RDACs with their corresponding EEMEM previously stored values. - Use a delay of 30us!!!
        #define EEMEM_read        0x90 //9 - Read contents of EEMEM (ADDR) from SDO output in the next frame. See Table 19. - Use a delay of 30us!!!
        #define gWiper            0xA0 //10 - Read RDAC wiper setting from SDO output in the next frame. See Table 20. - Use a delay of 30us!!!
        #define sWiper            0xB0 //11 - Write contents of Serial Register Data Byte 0 and Serial Register Data Byte 1 (total 10 bits) to RDAC (A0). See Table 14.
        #define Up6Db            0xC0 //12 - Increment by 6 dB: Left-shift contents of RDAC (A0),stop at all 1s. See Table 17.
        #define UpAll6Db        0xD0 //13 - Increment all by 6 dB. Left-shift contents of all RDAC registers, stop at all 1s.
        #define Up1                0xE0 //14 - Increment contents of RDAC (A0) by 1, stop at all 1s. See Table 15.
        #define Up1All            0xF0 //15 - Increment contents of all RDAC registers by 1, stop at all 1s.
        
        void storeEEMEM2RDAC(uint8_t w);
        void storeRDAC2EEMEM(uint8_t w);
        void setEEMEM(uint8_t w, uint16_t v);
        void stepDown6Db(uint8_t w);
        void stepDownAll6Db(void);
        void stepDown1(uint8_t w);
        void stepDown1All(void);
        void refreshAllRDAC(void);
        uint16_t getEEMEM(uint8_t w);
        uint16_t getWiper(uint8_t w);
        void setWiper(uint8_t w, uint16_t v);
        void stepUp6Db(uint8_t w);
        void stepUpAll6Db(void);
        void stepUp1(uint8_t w);
        void stepUp1All(void);
        float getTolerance(void);
        void repeatCMD(void);
        
    #ifdef __cplusplus
}
#endif
#endif /* __AD5235_H */

 

AD5235.c

As example you can create in your gpio.h the following macros for a Chip Select pin set on PA8

#define ResistorOn HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);
#define ResistorOff HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);

 

 

#include "AD5235.h"
#include "spi.h"
#include "gpio.h"
uint16_t ret = 0;
 
static void AD5235_write(uint8_t cmd, uint16_t val){
    uint8_t in[3] = {0, 0, 0};
    in[0] = cmd;
    in[1] = val >> 8;
    in[2] = val & 0xFF;
    ResistorOff;
    HAL_SPI_Transmit(&hspi2, in, 3, 100);
    ResistorOn;
}




static uint16_t AD5235_read(void){
    uint8_t in[3] = {0, 0, 0};
    uint8_t out[3] = {0, 0, 0};
    ResistorOff;
    HAL_SPI_TransmitReceive(&hspi2, in, out, 6, 100);
    ResistorOn;
    ret = (uint16_t)(out[1] << 8) + out[2];
    return ret;
}




//uint16_t transferData(uint8_t cmd, uint16_t val)
//{
//    uint8_t bytes[SEND_LIMIT], i;
//    CS_PressOff;
//    bytes[0] = cmd;
//    bytes[1] = val >> 8;
//    bytes[2] = val & 0xFF;
//    __HAL_LOCK(&hspi2);
//  for(i=0; i<SEND_LIMIT; i++)
//  {
//      // Wait until the transmit buffer is empty
//        while(__HAL_SPI_GET_FLAG(&hspi2, SPI_FLAG_TXE) == RESET){
//        }
//    // Send the byte
//        hspi2.Instance->DR = bytes[i];
//    // Wait to receive a byte
//        while(__HAL_SPI_GET_FLAG(&hspi2, SPI_FLAG_RXNE) != RESET){
//        }
//    // Return the byte read from the SPI bus
//    bytes[i] = hspi2.Instance->DR;
//  }    
//    __HAL_UNLOCK(&hspi2);
//    CS_PressOn;
//    return (uint16_t)(bytes[1] << 8) + bytes[2];
//}




void storeEEMEM2RDAC(uint8_t w) {
    AD5235_write(EEMEM2RDAC + w,  CMD_NOP);
} //1 - Restore EEMEM (A0) contents to RDAC (A0) register. See Table 16.




void storeRDAC2EEMEM(uint8_t w) {
    AD5235_write(RDAC2EEMEM + w,  CMD_NOP);
} //2 - Store wiper setting. Store RDAC (A0) setting to EEMEM (A0). See Table 15. - Use a delay of 50ms!!!




void setEEMEM(uint8_t w, uint16_t v) {
    AD5235_write(EEMEM_store + w, v);
} //3 - Store contents of Serial Register Data Byte 0 and Serial Register Data Bytes 1 (total 16 bits) to EEMEM (ADDR). See Table 18.- Use a delay of 50ms!!!/RDAC1 is 0, RDAC2 is 1, User1 is 2....User13 is 14




void stepDown6Db(uint8_t w) {
    AD5235_write(Down6Db + w,  CMD_NOP);
} //4 - Decrement by 6 dB. Right-shift contents of RDAC (A0) register, stop at all 0s.




void stepDownAll6Db(void) {
    AD5235_write(DownAll6Db , CMD_NOP);
} //5 - Decrement all by 6 dB. Right-shift contents of all RDAC registers, stop at all 0s.




void stepDown1(uint8_t w) {
    AD5235_write(Down1 + w, CMD_NOP);
} //6 - Decrement contents of RDAC (A0) by 1, stop at all 0s.




void stepDown1All(void) {
    AD5235_write(Down1All, CMD_NOP);
} //7 - Decrement contents of all RDAC registers by 1, stop at all 0s.




void refreshAllRDAC(void) {
    AD5235_write(AllRDAC, CMD_NOP);
} //8 - Reset. Refresh all RDACs with their corresponding EEMEM previously stored values. - Use a delay of 30us!!!




uint16_t getEEMEM(uint8_t w) {
    AD5235_write(EEMEM_read + w, CMD_NOP);
    //delay_us(30);
    HAL_Delay(1);
    return AD5235_read();
}//9 - Read contents of EEMEM (ADDR) from SDO output in the next frame. See Table 19. - Use a delay of 30us!!!




uint16_t getWiper(uint8_t w) {
    AD5235_write(gWiper + w, CMD_NOP);
    //delay_us(30);
    HAL_Delay(1);
    return AD5235_read();
    //transferData(0xA0 + w, CMD_NOP);
    //HAL_Delay(1);
    //return transferData(CMD_NOP, CMD_NOP);
} //10 - Read RDAC wiper setting from SDO output in the next frame. See Table 20. - Use a delay of 30us!!!




void setWiper(uint8_t w, uint16_t v) {
    AD5235_write(sWiper + w, v);
    //transferData(0xB0 + w, v);
} //11 - Write contents of Serial Register Data Byte 0 and Serial Register Data Byte 1 (total 10 bits) to RDAC (A0). See Table 14.




void stepUp6Db(uint8_t w) {
    AD5235_write(Up6Db, CMD_NOP);
} //12 - Increment by 6 dB: Left-shift contents of RDAC (A0),stop at all 1s. See Table 17.
void stepUpAll6Db(void) {
    AD5235_write(UpAll6Db, CMD_NOP);
} //13 - Increment all by 6 dB. Left-shift contents of all RDAC registers, stop at all 1s.
void stepUp1(uint8_t w) {
    AD5235_write(Up1 + w, CMD_NOP);
}//14 - Increment contents of RDAC (A0) by 1, stop at all 1s. See Table 15.
void stepUp1All(void) {
    AD5235_write(Up1All, CMD_NOP);
}//15 - Increment contents of all RDAC registers by 1, stop at all 1s.
void repeatCMD(void) {
    ResistorOff;
    ResistorOn;
}//16 - See page 21 in manual Another subtle feature of the AD5235 is that a subsequent CS strobe, without clock and data, repeats a previous command




float getTolerance(void)
{
    float tol = getEEMEM(15);
    int8_t b_1 = ((uint16_t)tol >> 8);
    int8_t b_0 = ((uint16_t)tol & 0xFF);
    if(b_1 > 127) //check if first bit in b_1 is 1
    b_1 -= 128;
    else
    b_1 = -b_1;
    for(uint8_t p = 0; p < 8; p++)
    {
        if((b_0 >> p) & 1)//check if but in position p is 1
        {
            tol =(float)b_1 + (float)b_0/ (float)(2 << p);//add the decimal part of the tolerance
            break;
        }
    }
    return tol;
}

 

 

Comments powered by CComment

Who’s online

We have 74 guests and no members online