VLT
®
FCD Series
■ Serial communication for FCD 300
■ Protocols
All frequency converters 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 Pro-
file, are:
• Profidrive protocol
• Danfoss FC protocol
To select Danfoss FC protocol, parameter 512 Tele-
gram Profile is set to FC protocol [1].
■ Telegram Traffic
C
ontrol and response telegrams
Telegram traffic in a master-slave system is con-
trolled 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 tele-
gram, addressed to that slave can send a response
telegram.
B
roadcast
A master can send the same telegram simultane-
ously 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 for-
mat (ADR), see Telegram structure.
C
ontent 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 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 frequency converter (ADR). Then fol-
lows a number of data bytes (variable, depending on
the type of telegram). The telegram is completed by
a data control byte (BCC).
Telegram times
The communication speed between a master and a
slave depends on the baud rate. The frequency con-
verter’s baud rate must be the same as the master’s
baud rate and be selected in parameter 501 Bau-
drate.
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
MG.04.A1.02 - VLT is a registered Danfoss trade mark
94
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