TANDELTA OQSExISG2, Руководство пользователя

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11.3 Modbus
To select Modbus as the preferred communication method, please use the PC/Laptop Software
and refer to the appropriate manual.
11.3.1 Hardware
The Tan Delta serial communication uses an RS485 multi-drop interface.
11.3.2 Configurable Parameters
The serial configuration must be set to 8 bits with no parity and will communicate at 9600 baud.
The OQS operates in a slave mode with a default ID of 1 which can be preset to suit on register
11 (0x0B), with the serial device which controls the communications (e.g. the monitoring
computer) acting as master and issuing commands to which the slave will reply. OQS will not
transmit any data except in response to a command from the master, and will expect no further
commands until the last command has been replied to.
11.3.3 Communication Mode
OQS supports communication using the OQS proprietary protocol which uses RS485 in ASCII mode
(not covered by this document), and Modbus RTU protocol which uses RS485 in Hex mode. The
suitable method of communication can be set by presetting register 12 (0x0C) to:
TDS RS485 1
ModBus RTU 2
11.3.4 Message Framing
Message start with a silent interval of at least 3.5 character times then the first field transmitted
is assumed to be the device address.
Following the last transmitted character, a similar interval of at least 3.5 character times marks
the end of the message. A new message can begin after this interval.
The entire message frame must be transmitted as a continuous stream. If a silent interval of
more than 1.5 character times occurs before completion of the frame, the receiving device
flushes the incomplete message and assumes that the next byte will be the address field of a
new message.
Similarly, if a message starts earlier than 3.5 character times following a previous message, the
receiving device will consider it a continuation of the previous message. This will set an error,
as the value in the final CRC field will not be valid for the combined messages.
A typical message format is shown below:
Start 3.5 Characters
Address 8 Bits
Function 8 Bits
Data 16 Bits
CRC 16 Bits