Serial Communication For Fc Protocol; Protocols; Telegram Communication; Telegram Build-Up Under Fc Protocol - Danfoss VLT 8000 AQUA series Operating Instructions Manual

Serial communication for FC protocol

Protocols

As standard, all VLT 8000 AQUA units have a RS 485
port which enables a choice among four protocols.
• FC
• Profibus*
• Modbus RTU*
• DeviceNet*
• LonWorks*
* Please note that these are option cards with
separate input terminals.

Telegram communication

Control and reply telegrams
The telegram communication in a master/slave system
is controlled by the master. A maximum of 31 slaves
can be connected to one master, unless a repeater
is used. If a repeater is used, a maximum of 126
slaves can be connected to one master.
The master continuously sends telegrams addressed
to the slaves and awaits reply telegrams from these.
The response time of the slaves is max. 50 ms.
Only a slave that has received a faultless
telegram addressed to that slave will response
by sending a reply telegram.
Broadcast
A master can send the same telegram at the same
time to all slaves connected to the bus. In such
broadcast communication, the slave does not send
a reply telegram to the master, provided the telegram
has been correctly received. Broadcast communication
is set up in the address format (ADR), see the next
page. Contents of a character (byte)
Each transferred character begins with a start
bit. Subsequently, 8 data-bits are transferred,
corresponding to one byte. Each character is secured
via a parity bit set to "1" when there is even parity (i.e.
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VLT 8000 AQUA
an even number of binary 1's in the 8 data-bits and
the parity bit combined). A character ends with a stop
bite and thus consists of a total of 11 bits.

Telegram build-up under FC protocol

Each telegram begins with a start character (STX) =
02 Hex, followed by a byte that gives the telegram
length (LGE) and a byte that gives the VLT address
(ADR). Then follows a number of data bytes (variable,
depending on telegram type). The telegram ends
with a data control byte (BCC).
Telegram times
The speed of communication between a master
and a slave depends on the baud rate. The
baud rate of the frequency converter must be
the same as the baud rate of the master and is
selected in parameter 502 Baudrate.
After a reply telegram from the slave, there must be
a minimum pause of 2 characters (22 bits) before
the master is able to send another telegram. At a
baudrate of 9600 kbaud, there must be a minimum
pause of 2.3 msec. After the master has completed
the telegram, the response time of the slave back
to the master will be max. 20 msec. and there will
be a minimum pause of 2 characters.
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