Hi!

We need to use custom structures of BITS (not BOOLs) in our projects. For example:

TYPE ST_3bit :
STRUCT
    x1: BIT;
    x2: BIT;
    x3: BIT;
END_STRUCT
END_TYPE

...and ST_7bit in the same way. This is mandatory due to requirements of certain devices.

I combine 3bit and 7bit with a further structure:

TYPE ST_3bit :
STRUCT
    x1: BIT;
    x2: BIT;
    x3: BIT;
END_STRUCT
END_TYPE

Then, I do a union of the combined structure with WORD.

TYPE U_Test :
UNION
    st3_7: ST_3bit_7bit;
    wTest: WORD;
END_UNION
END_TYPE

This doesn't work as I would expect. st3bit is copied to WORD correctly but st7bit is byte-aligned to the higher byte of the WORD.

Example: uUnionTest.st3_7.st3bit.x1 TRUE --> wTest is 256.

Is there any way I could pack the bits and omit the byte-alignment?

Please provide ST_3bit_7bit code (copy/paste issue). Providing the expected bit partern over a word would also help.

Hi,
here's ST_3bit_7bit:

TYPE ST_3bit_7bit :
STRUCT
    st3bit: ST_3bit;
    st7bit: ST_7bit;
END_STRUCT
END_TYPE

In pic1 the result is as expected.

In pic2 I would expect value 15.

I believe your issue is that the structure size is still a byte. I'm not sure if there is a better way but you might want to look into doing something like this (Instead of a union):

wTest := SHL((st7bit AND 2#01111111), 3) + (st3bit AND 2#00000111);