8 Communication
8.2 Modbus
142
SICAM I/O Unit, 7XV5673, Device Manual
E50417-H1040-C484-A3, Edition 05.2012
Number of Connections
Up to 4 TCP connections are possible:
•
Without user port number:
4 connections via standard port 502
•
With user port number:
2 connections via standard port 502 and 2 connections via the
user port
8.2.4
Modbus UDP
Properties Modbus UDP
•
Connectionless, asynchronous client-server communication via Ethernet protocol on the basis of UDP/IP
•
Use of IP addresses for addressing individual components connected to the Bus (bus stations)
•
Use of a parameterized port number (see Table 8-3)
•
All data types in the Modbus UDP telegrams that are bigger than 1 byte, are stored in the Big-Endian
format, that is, the most significant byte (MSB) is saved on the least significant register address and is
transferred first.
•
Sequence of the communication:
−
In order to start data transfer from server to client, the client sends a request to the server.
−
If the requested data is not available, the server sends the client the requested data or an error
feedback.
•
The Modbus data in the UDP telegram has a maximum size of 260 bytes:
−
Maximum of 253 bytes for data and
−
7 bytes for Modbus UDP header
The following parameters can be set for the Modbus UDP:
Table 8-3
Modbus UDP Settings
Parameter
Default Setting
Settings
IP address
192.168.0.55
Any,
0.0.0.0 for DHCP
Subnet mask
255.255.255.0
Any
Default gateway
192.168.0.1
Any
Bus protocol
Modbus UDP
-
Port number
51000
10000 to 65535
Access rights
Full
Full
Read only
Communication supervision time
8 * 10 ms
0 s = invalid
10 ms to 60 000 ms
MAN_SICAM_IO-Unit_7XV5673_US.book Page 142 Thursday, May 10, 2012 10:59 AM