LS Industrial Systems XGB Series - Modbus TCP;IP Server

Chapter6 Dedicated Service
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6.4 Modbus TCP/IP Server
Modbus TCP/IP server operates as below [Fig.6-6] Modbus TCP/IP Server operation flow.
Client
Time
①SYN
Time
②SYN ACK
③ACK
④PUSH ACK
PUSH ACK
⑥ACK
⑦FIN ACK
⑧ACK
⑨RST
Server
Transmission port : n >1024
Destination port: 502
Connection
Disconnection
Connection
Disconnection
Modbus TCP/IP protocol
(Client)
Modbus TCP/IP protocol
(Server)
Transmission port : n >1024
Destination port: 502
●
●
●
[Figure 6-6] Modbus TCP/IP Server operation flow
(4) Connection
(a) Client does transmit SYN① to serve. Server does SYN ACK.②
(b) Connection port no. is XGT dedicated protocol port no. 502.
(c) Client does connection check response ACK.③
(d) Finishing ~ makes client/server connection.①③
(5) TCP XGT client
(a) After connection, client does transmit PUSH ACK ac④ cording to XGT dedicated protocol.
(b) Server does transmit PUSH ACK for PUSH ACK Frame. ⑤
(c) Client does transmit ACK.⑥
(6) Disconnection
(a) Client does transmit DISCONNECTION.⑦
(b) Server does transmit RST and disconnect. ⑧