272
ICC
Figure 106: Modbus - Profibus Little Endian
13.2
Ex: Modbus - DeviceNet
This example shows the interaction between a network using an object value
method (Modbus) and one using a bag of bytes method (DeviceNet) to exchange
data. The gateway reads holding registers 1 and 2 from the Modbus network,
stores the data into the database, and then sends the 4 bytes of input data onto
the DeviceNet network. Figure 107 shows this data movement for the gateway’s
database configured as little endian. Because the DeviceNet specification defines
multi-byte values within the byte array to be interpreted as little endian, it is
recommended that the database be configured for little-endian byte order when
using DeviceNet. In the example, holding register 1 has a value of 0x1234 and
holding register 2 has a value of 0x5678. When the DeviceNet device receiving
the input data from the gateway recombines the two pairs of 2-byte values, the
resulting data is 0x1234 and 0x5678, thus successfully receiving the correct
values for holding registers 1 and 2.
Figure 107: Modbus - DeviceNet Little Endian
