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The float value isn't correct in union

John Song43
Intellectual 470 points
Other Parts Discussed in Thread: TMS320F28377S

Hi,

I used union is TMS320F28377S launchpad. But the float value isn't correct. 

union {
       float32 F_Data;
       Uint8 B_Date[4];
}Data1;

The HEX value of float 3.56 should be 0x4063d70a. I put these value into array. But the float value is not 3.56 (0x4063d70a). it change to 0x00d7000a. I appreciate if you tell me how to correct this issue. Thanks.

Regards,

John

  • 0
    TI__Mastermind 27200 points
    John,

    The minimum data width on C28x is 16-bits. When you specify a char variable which might be 8-bits wide on some machines, it actually occupies 16-bits of memory on C28x. This is why the Hex value for each element of "B_Date" shows as 16-bits in the CCS expressions window and watch window.

    To represent 3.56f in the structure, you'll need only 2 elements:
    Data1.B_Date[0] = 0xD70A;
    Data1.B_Date[1] = 0x4063;

    Depending on what you're doing , there are compiler intrinsics to access byte data which may be helpful. Please see section 7.5.6 of the C28x Compiler User's Guide (spru514j): www.ti.com/.../spru514j.pdf

    Regards,

    Richard