User manual

2.1.2.10 MODBUS/TCP Port
Applications which use the TCP/IP protocol while communicating over the internet
require a preassigned port number. Some of these port number may already be
appointed to other processes. For example, port 80 is reserved for HTTP and port 23
is reserved for TELNET. For MODBUS/TCP protocol, this port number is assigned
as 502. It isn't mandatory for the MODBUS/TCP applications to communicate using
this port but the software applications must support this port too.
2.1.2.11 Link
Select the link mode according to the network configuration to which the EMG
Series device will be connected.
2.1.3 Operating Modes
EMG Software is able to communicate over TCP protocol using two operating modes. The
packet structures and communication is explained next.
2.1.3.1 MODBUS/TCP Packet Structure
MODBUS/TCP protocol is a revised version of the existing MODBUS protocol to enable
communication over the internet. The MODBUS protocol which is used in serial
communication applications has a packet structure as shown in Figure 1.
Figure 1. Modbus Packet Structure
“Device Address” defines the address of the device on the network to which the received
queries will be sent. This address must be different for each device on the RS-485/232
network. “Function Code” is one of the function codes defined in the MODBUS standard.
“Data” is the data block which contains the information requested from the device or sent by
the device. “Error Check (CRC)” defines the 16 bit long CRC information which is used to
verify the data integrity.