Inhaltsverzeichnis
Werbung
Verfügbare Sprachen
Verfügbare Sprachen
7
Modbus over Ethernet
7.1
Modbus/TCP
Modbus/TCP uses the Ethernet interface for communicating with the Modbus data.
The Modbus telegrams are transmitted via an Ethernet network (IEEE 802.3) using the
TCP protocol of the TCP/IP protocol family. The Versatronic is operated exclusively as a
slave. A master can query all device variables according to the Modbus address tables for
this slave.
Ä Chapter 8 'Modbus address tables' on page 41.
ð
For querying a master via Modbus/TCP on the Versatronic the following aspects must be
considered:
n
the TCP port for Modbus in the Versatronic is permanently set to 502
n
Queries must be set to the correct target IP address of the Versatronic
n
the UNIT ID (device address) for Modbus in the Versatronic is permanently set to 255
NOTICE!
Only two Modbus masters (clients) can access this slave (server)
simultaneously via Modbus/TCP. A connection opened by a master is
closed by the slave after 30 seconds of inactivity.
If a Modbus/TCP port is closed (by a slave or from the opposite end), it can
only be reopened after 10 seconds have elapsed.
Structure of a Modbus/TCP telegram
Modbus/TCP is a standardized process, in which a Modbus telegram is encapsulated in a
TCP segment and transmitted via Ethernet.
The Modbus telegram (without CRC) is transmitted with an additional 6 or 7 byte
"MBAP header" (Modbus Application Header). The seventh byte corresponds to the first
serial byte, but has a different designation here.
MBAP header
2 bytes Transaction
ID
Identical in request
and response
For comparison: The "normal" Modbus telegram
Slave address 1 byte
Using this protocol, a suitable process data visualization program can read and write
system values over a company's own Ethernet network, for example. All device variables
from the Modbus address tables can be accessed.
Ä Chapter 8 'Modbus address tables' on page 41.
ð
2 bytes Protocol ID
2 bytes Length
Length of request/
Must be 0 for
response in bytes
Modbus
starting with (incl.)
Function code 1 byte
39
Modbus over Ethernet
1 byte Unit ID
Corresponds to the
device address and
must be 0xFF or 255
"Unit ID"
for Modbus/TCP
Data field x bytes
Modbus telegram
Additional bytes as
below, but without
CRC
CRC16 2 bytes
417102397 Rev. 1-10.2019
Werbung
Kapitel
Inhaltsverzeichnis
