Algotithm to Convert 4 byte Hex to 32 bit float

 I really struggled hard to find out some sorts of algorithm to convert 4 hex bytes to 32 bit float for my requirement on some analysis of MODBUS protocol. I didn’t find it and it tok me nearly 2 days to design this. Here is the algorithm..

float ModbusRead(byte id,byte msbAddress,byte lsbAddress,byte msbCrc,byte lsbCrc)
{
num=1.00;
Serial.write(id);
Serial.write(0x03);
Serial.write((byte)msbAddress);
Serial.write((byte)lsbAddress);
Serial.write((byte)0x00);
Serial.write(0x02);
Serial.write(msbCrc);
Serial.write(lsbCrc);
delay(1000);

for(i=0;i<9;i++)
{
if(!Serial.available())
{
for (int x=0;x < 9;x++)
{
reply[x]=0x00;
}
while(Serial.available()){}
break;
}
reply[i]=Serial.read();
}
while(Serial.available()){}
if((reply[3] & 0x80)!=0)
num=num*-1;
reply[3]=reply[3]<<1;
if((reply[4] & 0x80)!=0x00)
reply[3]=reply[3] | 0x01;
num=num*pow(2,reply[3]-0x7F);
i=0;
delay(1000);
return num*calculatemantisa(reply[4],reply[5],reply[6]);
}
float calculatemantisa(byte a,byte b,byte c)
{
float x=1.0000;
if((a & 0x40)!=0x00)
x=x+pow(2,-1);
if((a & 0x20)!=0x00)
x=x+pow(2,-2);
if((a & 0x10)!=0x00)
x=x+pow(2,-3);
if((a & 0x8)!=0x00)
x=x+pow(2,-4);
if((a & 0x4)!=0x00)
x=x+pow(2,-5);
if((a & 0x2)!=0x00)
x=x+pow(2,-6);
if((a & 0x1)!=0x00)
x=x+pow(2,-7);

if((b & 0x80)!=0x00)
x=x+pow(2,-8);
if((b & 0x40)!=0x00)
x=x+pow(2,-9);
if((b & 0x20)!=0x00)
x=x+pow(2,-10);
if((b & 0x10)!=0x00)
x=x+pow(2,-11);
if((b & 0x8)!=0x00)
x=x+pow(2,-12);
if((b & 0x4)!=0x00)
x=x+pow(2,-13);
if((b & 0x2)!=0x00)
x=x+pow(2,-14);
if((b & 0x1)!=0x00)
x=x+pow(2,-15);

if((c & 0x80)!=0x00)
x=x+pow(2,-16);
if((c & 0x40)!=0x00)
x=x+pow(2,-17);
if((c & 0x20)!=0x00)
x=x+pow(2,-18);
if((c & 0x10)!=0x00)
x=x+pow(2,-19);
if((c & 0x8)!=0x00)
x=x+pow(2,-20);
if((c & 0x4)!=0x00)
x=x+pow(2,-21);
if((c & 0x2)!=0x00)
x=x+pow(2,-22);
if((c & 0x1)!=0x00)
x=x+pow(2,-23);

return x;
}
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Bikash Panda

Blogger / Embedded System Developer at WGLabz
A techie, tinkerer and tech lover, who loves to blog and feels everyone can learn tech provided they have the right attitude towards learning and passion. By profession, I am an IOT developer working in Smart Home/ Smart Grid domain.
Bikash Panda
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