Serial Communication For Fcd 300 - Danfoss VLT DMS 300 Manual

Serial communication for FCD 300

Protocols
All variable frequency drives are equipped with an
RS 485 port as standard, which makes it possible to
choose between two protocols. The two protocols that
can be selected in parameter 512 Telegram Profile , are:
• Profidrive protocol
• Danfoss FC protocol
To select Danfoss FC protocol, parameter 512
Telegram Profile is set to FC protocol [1].
Telegram Traffic
Control and response telegrams
Telegram traffic in a master-slave system is controlled
by the master. A maximum of 31 slaves can be
connected to a master, unless repeaters are used.
If repeaters are used, a maximum of 126 slaves
can be connected to a master.
The master constantly sends telegrams addressed to
the slaves and waits for response telegrams from them.
The slave's response time is a maximum of 50 ms.
Only a slave that has received an error-free telegram,
addressed to that slave can send a response telegram.
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 back to the master as to
whether the telegram has been 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 at "1" when it reaches parity (i.e. when
there is an equal number of 1's in the 8 data bits and
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the parity bit in total). A character is completed by
a stop bit, thus consisting of 11 bits in all.
Telegram Structure
Each telegram begins with a start character (STX) =
02 Hex, followed by a byte that denotes the length
of the telegram (LGE) and a byte that denotes the
address of the adjustable frequency drive (ADR).
Then follows a number of data bytes (variable,
depending on the type of telegram). The telegram
is completed by a data control byte (BCC).
Telegram timing
The communication speed between a master and a
slave depends on the baud rate. The variable frequency
drive's baud rate must be the same as the master's
baud rate and be selected in parameter 501 Baudrate.
After a response telegram from the slave, there
must be a pause of at least 2 characters (22 bits)
before the master can send a new telegram. At a
baud rate of 9600 baud there must be a pause of
at least 2.3 ms. When the master has completed
the telegram, the slave's response time back to
the master will be a maximum of 20 ms, and there
will be pause of at least 2 characters.
Pause time, min: 2 characters
Response time, min: 2 characters
Response time, max: 20 ms
The time between the individual characters in a telegram
may not exceed 2 characters and the telegram must
be completed within 1.5 x nominal telegram time. At
a baud rate of 9600 baud and a telegram length of 16
bytes the telegram will be completed after 27.5 msec.
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