ESP32 ADXL345 doesn't get the negative values - arduino

Question

Hi I can run this code without any problem on Arduino UNO. My output is like : 0.05 0.10 1.01
But when I run this code on ESP32, my output is : 255.89 255.81 0.99 and I don't see any minus value. What is the problem?
ESP32's X,Y,Z raw values like : 6500 0 , 65000 , 1 . ESP32 can't get the negative values. I have to do something with wire.h and I need to change uint8_t or uint16_t something but I really don't understand how should I solve this problem.
#include <Wire.h> // Wire library - used for I2C communication
int ADXL345 = 0x53; // The ADXL345 sensor I2C address
float X_out, Y_out, Z_out; // Outputs
float X, Y, Z ;
void setup() {
Serial.begin(115200); // Initiate serial communication for printing the results on the Serial monitor
Wire.begin(); // Initiate the Wire library
// Set ADXL345 in measuring mode
Wire.beginTransmission(ADXL345); // Start communicating with the device
Wire.write(0x31);
Wire.write(0x0B);
Wire.endTransmission();
Wire.beginTransmission(ADXL345);
Wire.write(0x20); // Z-axis offset register
Wire.write(-7);
Wire.endTransmission();
Wire.beginTransmission(ADXL345);
Wire.write(0x2D); // Access/ talk to POWER_CTL Register - 0x2D
// Enable measurement
Wire.write(0x08); // (8dec -> 0000 1000 binary) Bit D3 High for measuring enable
Wire.endTransmission();
Wire.beginTransmission(ADXL345);
Wire.write(0x2C);
// Enable measurement
Wire.write(0x09); //For low power 000x x pin set to 1 /1001 determine Hz
Wire.endTransmission();
delay(10);
}
void loop() {
unsigned long Time = millis();
// === Read acceleromter data === //
Wire.beginTransmission(ADXL345);
Wire.write(0x32); // Start with register 0x32 (ACCEL_XOUT_H)
Wire.endTransmission(false);
Wire.requestFrom(ADXL345, 6, true); // Read 6 registers total, each axis value is stored in 2 registers
X_out = ( Wire.read() | Wire.read() << 8); // X-axis value
X = X_out /256; //For a range of +-2g, we need to divide the raw values by 256, according to the datasheet
Y_out = ( Wire.read() | Wire.read() << 8); // Y-axis value
Y = Y_out /256;
Z_out = ( Wire.read() | Wire.read() << 8); // Z-axis value
Z = Z_out /256;
delay(20);
Serial.print(X);
Serial.print(" ");
Serial.print(Y);
Serial.print(" ");
Serial.print(Z);
Serial.println(" ");
}

Answer 1

On the Arduino Uno there are 16-bit integers. The ADXL345 seems to receive this data format. Therefore everything plays out nicely. You are using 32-bit integers on the ESP32. Therefore you have to choose the right data type explicitly. Otherwise the negative numbers appear in the positive region.
The execution order of the Wire.read()-calls is not defined in your code. Therefore the compiler may join the bytes 0xAA and 0xBB to 0xAABB or 0xBBAA. You should add a sequence point to make sure that the code does what's intended.
I have not tested this code. That should be the correct order, in case I got the datasheet description right:
int16_t readInt16()
{
int lsb = Wire.read();
int msb = Wire.read();
return int16_t(lsb | msb << 8);
}
X_out = readInt16() / 256.f;
Y_out = readInt16() / 256.f;
Z_out = readInt16() / 256.f;