Pilz PNOZ mmc1p ETH - Manual (Page 9)

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2-1
2.1 Modbus/TCP - Basics
2 Communication via Modbus/TCP
2 2000 Communication via Modbus/TCP Communication via Modbus/TCP 2- 2.1 Modbus/TCP - Basics 2100 Modbus/TCP - Basics 2- ModbusTCP_Modbus/TCP Allg-1
Modbus is an open fieldbus standard published by the User Group
MODBUS-IDA (see www.Modbus-IDA.org).
Modbus/TCP is a protocol based on Industrial Ethernet (TCP/IP over
Ethernet). It is a protocol with Client/Server communication. Data is
transferred via a request/response mechanism using function codes
(FC).
Modbus/TCP is connection-oriented, i.e. before usable data is trans-
ferred via Modbus/TCP, a connection must first be established between
two Modbus/TCP interfaces. The initiator of the connection is called the
Client. The communications partner with which the Client establishes
the connection is called the Server. Whether a connection on a device
assumes the role of Client or Server is defined when a connection is con-
figured. As a result, the Server/Client role only applies for the used con-
nection.
Application Layer
Protocol
Modbus/TCP
TCP
(RFC 793)
IP
(RFC 791)
Industrial Ethernet
Physical Layer
Ethernet