Lenze I/O system 1000 System Manual - Manual (Page 715)

Modbus TCP Kommunikation
About Modbus TCP
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Modbus TCP: Modbus TCP is a Modbus RTU protocol where TCP/IP packets are transmitted.
The Modbus protocol is a communication protocol that supports a hierarchical structure
with one master an several slaves.
Modbus TCP expands Modbus by a client/server communication where several clients can
access a server. Since addressing is made via IP addresses, the address embedded in the
Modbus frame is irrelevant. The CRC checksum is not required either since protection takes
place via TCP/IP. After a request from a client, it waits for the response of the server until
an adjustable waiting time has elapsed.
With Modbus TCP, the RTU format is used exclusively: Here, each byte is transmitted as a
character. Thus, you have a higher data throughput as in the Modbus−ASCII format. RTU
time monitoring does not occur since the header includes the size of the frame length to
be received.
Data that is transferred with ModbusTCP may contain bit and word information. Here, in
case of bit chains, the most significant bit is transmitted first, which means it has the
left−most position in a word. In case of words, the most significant bit is transmitted first.
A Modbus slave is accessed via function codes (
¶ 719).