MCP41100 digital potentiometer with Arduino/STM32

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//STM32-based digital potmeter
#include <SPI.h> //SPI comunication


int analogValue_1;
int analogValue_2;

const byte analogInputPin_1 = PA0;
const byte analogInputPin_2 = PA1;

const byte CS1_pin = PA4; //CS pin for potmeter 1
const byte CS2_pin = PB9; //CS pin for potmeter 2

float rwa_1;
float rwa_2;
float rwb_1;
float rwb_2;

int counter_1 = 0; //counter for the potmeter 1
int counter_2 = 256; //counter for the potmeter 2

void setup()
{
 Serial.begin(9600);
 Serial.println("MCP41100");

 pinMode(CS1_pin, OUTPUT); //Chip select is an output
 pinMode(CS2_pin, OUTPUT); //Chip select is an output

 digitalWrite(CS1_pin, HIGH);
 digitalWrite(CS2_pin, HIGH);

 SPI.begin();
}

void loop()
{

  writePotmeter_1();
  writePotmeter_2();

  delay(300);

  readAnalogPin_1();
  readAnalogPin_2();

  counter_1++;
  counter_2--;

  if(counter_1 > 256) //this is for the increasing counter
  {
  counter_1 = 0;
  }

  if(counter_2 < 1)  //this is for the decreasing counter
  {
  counter_2 = 256;
  }

}

void writePotmeter_1()
{
    //CS goes low
    digitalWrite(CS1_pin, LOW);

    SPI.transfer(0x11);  //command 00010001 [00][01][00][01]
    SPI.transfer(counter_1);

    delayMicroseconds(100);
    Serial.print("counter_1: ");
    Serial.println(counter_1);

    //CS goes high
    digitalWrite(CS1_pin, HIGH);

}

void writePotmeter_2()
{

    digitalWrite(CS2_pin, LOW);

    SPI.transfer(0x11);  //command 00010001 [00][01][00][11]
    SPI.transfer(counter_2);

    delayMicroseconds(100);
    Serial.print("counter_2: ");
    Serial.println(counter_2);
    //End of transaction

    //CS goes high
    digitalWrite(CS2_pin, HIGH);
}

void readAnalogPin_1()
{
  analogValue_1 = analogRead(analogInputPin_1);
  Serial.print("Analog_1: ");
  Serial.println(analogValue_1);

  //Calculate resistance
  rwa_1 = (100000 * (256 - counter_1)/256) + 125;
  rwb_1 = (100000 * (counter_1)/256) + 125;

  Serial.print("rwa_1: ");
  Serial.println(rwa_1);
  Serial.print("rwb_1: ");
  Serial.println(rwb_1);
  Serial.print("sum: ");
  Serial.println(rwa_1+rwb_1);

}

void readAnalogPin_2()
{
  analogValue_2 = analogRead(analogInputPin_2);
  Serial.print("Analog_2: ");
  Serial.println(analogValue_2);


  //Calculate resistance
  rwa_2 = (100000 * (256 - counter_2)/256) + 125;
  rwb_2 = (100000 * (counter_2)/256) + 125;

  Serial.print("rwa_2: ");
  Serial.println(rwa_2);
  Serial.print("rwb_2: ");
  Serial.println(rwb_2);
  Serial.print("sum: ");
  Serial.println(rwa_2+rwb_2);

}


/*
 *  Resistance formula
 *  R = 100 kOhm *(256-x)/256 + Rw
 *  Rw = 125 for the 100 kOhm
 *  Check datasheet, because Rw depends on the VDD
 */