Data Exchange - HMS Anybus X-gateway Modbus-TCP User Manual

2.5 Data Exchange

Each of the two network interfaces exchanges data on its network through two buffers. The X-gateway
forwards the data between these buffers as shown below. Note that this process is separated from the
network data exchange. While the X-gateway ensures data consistency (where applicable), it does not
feature any built-in mechanisms for synchronization between the two Modbus-TCP networks.
Data To
the Modbus-TCP
Network
Modbus-TCP Network Interface
Data From
the Modbus-TCP
Network
Each buffer holds a maximum of 256 bytes of data. The first two bytes in either direction can be dedi-
cated for control/status information, and another eight bytes of data coming from Network 2 can fea-
ture a live list.
Through the dedicated control word, the client on Network 1 starts/stops the exchange of data on Net-
work 2, and also resets the X-gateway if needed. The client on Network 1 can see the status of Network
2 in the corresponding status word. The live list feature gives the client on Network 1 the opportunity
to continuously see and monitor the status of each individual transaction on Network 2.
The amount of data that shall be exchanged, and the use of the control/status word and the live list, is
specified separately for each application. This means that even though up to 256 bytes of data can be
potentially forwarded to an interface, the amount of data that will actually be exchanged on that network
is determined by the settings in the configuration web pages.
The available control/status functionality is described below. Also note that the terminology and defi-
nitions used for different types of data vary greatly between different networking systems. All data trans-
ported through the Anybus X-gateway for Modbus-TCP - Modbus-TCP is simply referred to as 'I/O
data' in this document.
Anybus X-gateway for Modbus-TCP - Modbus-TCP
Doc.Rev. 1.00
Anybus X-gateway for Modbus-TCP - Modbus-TCP 12
Status Word
Data From
the Modbus-TCP
Network
Industrial Network Interface
Control Word
Data to
the Modbus-TCP
Network
Doc.Id. SCM-1200-114