Lenze I/O system 1000 - Page 571

10 Modbus TCP communication
10.1 About Modbus TCP
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Lenze · I/O system 1000 · Reference Manual · DMS 5.0 EN · 09/2016 · TD17
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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 Modbus TCP 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
Function codes
( 575)