Protocols; Telegram Traffic; Telegram Structure - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide
Serial communication via RS 485 Interface
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Protocols

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Master-slave communication.

Telegram Traffic

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Control and response telegrams
The master controls telegram traffic in a master-slave system. A maximum of 31 slaves
can be connected to a master without the use of repeaters. With repeaters it is possible
to connect a maximum of 126 slaves to a master.
The master constantly sends telegrams addressed to the slaves and waits for their response
telegrams. The slave response time is maximum 50 ms.
A slave can only send a response telegram if it has received an error-free telegram addressed to itself.
Broadcast
A master can send the same telegram simultaneously to all slaves connected to the bus. During this broadcast
communication, the slave does not send any response telegrams to the master on whether the telegram is
correctly received. Broadcast communication is set up in address format (ADR), see Telegram structure.
Content of a character (byte)
Each character transferred begins with a start bit.
Then 8 data bits are transferred, corresponding to
a byte. Each character is secured via a parity bit,
which is set to "1" when it reaches parity (i.e. when
there is an equal number of 1's in the 8 data bits
and the parity bit in total). A character is completed
by a stop bit, thus consisting of 11 bits in all.

Telegram Structure

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Each telegram begins with a start character
(STX) = 02 Hex, followed by a byte denoting
the telegram length (LGE) and a byte denoting
the adjustable frequency drive address (ADR).
A number of data bytes (variable, depending on
the type of telegram) follow. The telegram is
completed by a data control byte (BCC).
* default setting ( )
How to Program
display text [ ] value for use in communication via serial communication port
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