Modbus/TCP 5-5
© 2005 HMS Industrial Networks
AB7665 User manual
I/O Data Format
The Anybus-X transfers I/O data between Modbus/TCP and J1939 without regard
to data content or format. Due to this, the user is responsible for making sure that
the devices on either network understand the format of the data.
J1939 is a little endian protocol; values are transmitted least significant byte first.
Hence, all data in the I/O tables is assumed, by the J1939 nodes, to be stored as lit-
tle endian.
Modbus/TCP is a big endian protocol; values are transmitted most significant byte
first.
The Swap I/O Bytes option in the J1939 Network Configuration pane of BWCon-
fig will swap the bytes of each 16-bit word in the I/O data tables. This will aid in
the transformation between the big and little endian networks. However, care must
be taken to assure that data is mapped to 16-bit work boundaries in order for this
feature to be fully effective.
