Lika EM58 MB, Руководство пользователя

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specified by function codes. The function code is sent from a
Client to the Server and indicates which kind of action the
Server must perform. MODBUS function codes are elements of
MODBUS request/reply PDUs.
The function code field of a MODBUS data unit is coded in one
byte. Valid codes are in the range of 1 ... 255 decimal (the
range 128 – 255 is reserved and used for exception responses).
Function code "0" is not valid. Lika devices only implement
public function codes.
Holding register In the MODBUS data model, a Holding register is the output
data. A Holding register has a 16-bit quantity, is alterable by
an application program, and allows either read-write or read-
only access.
IEEE 1588 This standard defines a protocol enabling synchronisation of
clocks in distributed networked devices (e.g. connected via
Ethernet).
Input register In the MODBUS data model, an Input register is the input
data. An Input register has a 16-bit quantity, is provided by an
I/O system, and allows read-only access.
LRC Checking
In ASCII mode, messages include an error–checking field that
is based on a Longitudinal Redundancy Checking (LRC)
calculation that is performed on the message contents,
exclusive of the beginning ‘colon’ and terminating CRLF pair
characters. It is applied regardless of any parity checking
method used for the individual characters of the message.
Master A Master is any network device that sends data requests to
Slaves.
Message The MODBUS messaging service provides a Client/Server
communication between devices connected on the 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.
MODBUS Response A MODBUS Response is the Response message sent by the
Server.
Network Network is a group of computers on a single physical network
segment.