User Manual
Modbus TCP/EtherNet IP Gateway
GT200-MT-EI
WWW.SSTCOMM.COM
33
5 Working Principle of Modbus TCP Master
Ethernet supports Modbus TCP function, described as below:
Data exchange of Modbus TCP and EtherNet/IP of GT200-MT-EI is set up through “mapping”. There are
two data buffer areas, one is EtherNet/IP network input buffer and the other is EtherNet/IP network output buffer.
Network input and output buffer is all for EtherNet/IP master. When the gateway is Modbus TCP master, Modbus
read command will write the read data to the network input buffer for EtherNet/IP accessing. Modbus write
register command gets data from network output buffer and export to the Modbus TCP slave equipment through
write command.
As is shown above: network input buffer range is 0x0000~0x01EB (function code 01H, 02H, 03H, 04H as
data input; function 05H, 06H, 15H, 16H as local data exchange); Network output buffer range is
0x4000~0x41EB (function code 05H, 06H, 15H, 16H as data output).
Ethernet can support configuring at most 48 commands, each one can read one group of continuous Modbus
registers.
