#include < SPI.h >

const int X8 = 0x06;
const int Y8 = 0x07;
const int Z8 = 0x08;

/*
bits
1 0  mode 00: standby, 01: measurement
5     1: spi 3 wire, 0: 4 wire
4      self test
3     2 glevel: 01 2g
1 0  mode, 00 standby, 01 measurement
*/
const int MODE = 0x16;

const int STATUS = 0x09;

//7 digital filter band width, 0 62.5 Hz, 1 125 Hz
const int CONTROL = 0x18;

bool isTesting = false;

const int chipSelectPin = 7;

void setup() {
    Serial.begin(9600);
    SPI.begin();
    pinMode(chipSelectPin, OUTPUT);

    //set up standby, spi 4 wire, 2g range,
    writeRegister(MODE, 0x04);

    //set up speed
    writeRegister(CONTROL, 0x00);

    delay(100);
}
void loop() {
    if (getSerial() == 't') {
        isTesting = true;
        writeRegister(MODE, 0x05); // 0000 0101- 0001 0101 0x15
        testing();

    }

}
void testing() {
    while (isTesting) {
        if ((readRegister(STATUS) & 1) == 1) {
            Serial.print((char) readRegister(X8), DEC);
            Serial.print("x");
            Serial.print((char) readRegister(Y8), DEC);
            Serial.print("y");
            Serial.print((char) readRegisterChar(Z8), DEC);
            Serial.print("z");
        }

        if (getSerial() == 'u') {
            isTesting = false;
            writeRegister(MODE, 0x04);
        }
    }
}
char getSerial() {
    if (Serial.available()) {
        char c = Serial.read();
        return c;
    }
    return 'x';
}
byte readRegister(byte thisRegister) {
    byte inByte = 0;
    SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE0)); // 500khz clock
    digitalWrite(chipSelectPin, LOW);
    SPI.transfer(thisRegister << 1);
    inByte = SPI.transfer(0x00);
    digitalWrite(chipSelectPin, HIGH);
    return inByte;
}
char readRegisterChar(byte thisRegister) {
    char inChar = 0;
    SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE0)); // 500khz clock
    digitalWrite(chipSelectPin, LOW);
    SPI.transfer(thisRegister << 1);
    inChar = SPI.transfer(0x00);
    digitalWrite(chipSelectPin, HIGH);
    return inChar;
}
void writeRegister(byte thisRegister, byte value) {
    SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE0)); // 500khz clock
    digitalWrite(chipSelectPin, LOW);
    SPI.transfer(128 | thisRegister << 1);
    SPI.transfer(value);
    digitalWrite(chipSelectPin, HIGH);
}

const int X10_LSB = 0x00;
const int X10_MSB = 0x01;
const int Y10_LSB = 0x02;
const int Y10_MSB = 0x03;
const int Z10_LSB = 0x04;
const int Z10_MSB = 0x05;

//[...]

void testing() {
        while (isTesting) {
            if ((readRegister(STATUS) & 1) == 1) {

                int xData = (readRegister(X10_MSB) << 8) | readRegister(X10_LSB);

                // checks if bit 9 is 1 and sign extends
                if ((xData & 512) == 512)
                    xData = (0b1111110000000000 | xData);
                int yData = (readRegister(Y10_MSB) << 8) | readRegister(Y10_LSB);
                if ((yData & 512) == 512)
                    yData = (0b1111110000000000 | yData);
                int zData = (readRegister(Z10_MSB) << 8) | readRegister(Z10_LSB);
                if ((zData & 512) == 512)
                    zData = (0b1111110000000000 | zData);

                Serial.print(xData);
                Serial.print("x");
                Serial.print(yData);
                Serial.print("y");
                Serial.print(zData);
                Serial.print("z");

            }

int xData =(readRegister (X10_LSB));
        xData = xData | (readRegister (X10_MSB)<<8);
        xData = xData << 6;
        int yData =(readRegister (Y10_LSB));
        yData = yData | (readRegister (Y10_MSB)<<8);
        yData = yData << 6;
        int zData = (readRegister (Z10_LSB));
        zData = zData | (readRegister (Z10_MSB)<<8);
        zData = zData << 6;

        xData /= 64;
        yData /= 64;
        zData /= 64;