Lika EMC58 MT, User Manual

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message to follow.
•
Unit Identifier: 1 byte set by the Client and echoed by
the Server for identification of a remote slave
connected on a serial line or on other buses.
Refer to page 35.
Media Access Control
(MAC) One of the sub-layers of the Data Link Layer that controls who
gets access to the medium to send a message.
Message The MODBUS messaging service provides a Client/Server
communication between devices connected on the Ethernet
TCP/IP network. The Client / Server model is based on four
types of messages:
•
MODBUS Request
•
MODBUS Confirmation
•
MODBUS Indication
•
MODBUS Response
The MODBUS messaging services are used for information
exchange.
MODBUS Confirmation A MODBUS Confirmation is the Response Message received on
the Client side.
MODBUS Indication A MODBUS Indication is the Request message received on the
Server side.
MODBUS Request A MODBUS Request is the message sent on the network by the
Client to initiate a transaction. Refer to page 37.
MODBUS Response A MODBUS Response is the Response message sent by the
Server. Refer to page 37.
Network Network is a group of computers on a single physical network
segment; otherwise it is an IP network address range that is
allocated by a system administrator.
Network address An IP address with a host portion that is all zeros.
Octet An 8-bit number, 4 of which comprise a 32-bit IP address.
They have a range of 00000000-11111111 that correspond to
the decimal values 0- 255.
Packet A unit of data passed over a TCP/IP network or wide area
network.
PDU The Protocol Data Unit (PDU) is the MODBUS function code
and data field in their original form. It is packed together with
the MBAP Header to form the Application Data Unit (ADU).
The MODBUS protocol defines three PDUs. They are:
•
MODBUS Request PDU, mb_req_pdu
•
MODBUS Response PDU, mb_rsp_pdu
•
MODBUS Exception Response PDU,
mb_excep_rsp_pdu
Refer to page 37.
Port It is an address that is used locally at the transport layer (on
one node) and identifies the source and destination of the