Why a Word (or INT) starts from the second byte?

Hi everybody,

I know the question can sound a bit "stupid" for most of the people here, but I wasn't able to find the answer to my question. Some minutes ago I was typing all the bit from M10.0 to M11.7, so it's like MW10. Then I forced MW10 to the value 1, here the surprise. The bit that has changed "state" was M11.0 insted of M10.0 as I  expected. Why Siemens start from the second byte ? Is there a reason?

Hello,

this called Byte-Order (Endianness).
Siemens SPS S-300/s7-400 use Big-Endian.

Regards

Christoph

sbartoc

Hi everybody,

I know the question can sound a bit "stupid" for most of the people here, but I wasn't able to find the answer to my question. Some minutes ago I was typing all the bit from M10.0 to M11.7, so it's like MW10. Then I forced MW10 to the value 1, here the surprise. The bit who that has changed "state" was M11.0 insted of M10.0 as I  expected. Why Siemens start from the second byte ? Is there a reason?

Hello sbartoc,

Have a look this thread in particular fritz:

Memory Representation - Entries - Forum - Industry Support - Siemens