FCM 300 Series
75
MG.03.B6.02 - VLT is a registered Danfoss trademark
■ Telegram build-up
Each telegram begins with a startbyte (STX) = 02
Hex, followed by a byte that gives the telegram length
(LGE) and a byte that gives the address (ADR).
Then follows a number of databytes (variable,
depending on telegram type). The telegram ends with
a data control byte (BCC).
STX LGE ADR Data BCC
■ Serial bus
Master
Slave 31 (126)
Slave 2
Slave 1
Address 1
Address 2 Address 31 (126)
Serial bus
■ Telegram communication
Control and reply telegrams
The telegram communication in a master/slave
system is controlled by the master. A maximum of 31
slaves (FC motors) can be connected to one master,
unless a repeater is used - see also the description of
the address format.
The master continuously sends control telegrams
addressed to the slaves and awaits reply telegrams
from these. The response time of the slaves is
maximum 50 ms.
Only a slave that has received a faultless telegram
addressed to that slave will respond by sending back
the telegram unchanged.
Broadcast
A master can send the same telegram at the same
time to all slaves connected to the bus. In such
broadcast communication, the control telegram
broadcast bit of the address bit has a value of 1 (see
VLT address). Address bits 0-4 are not used.
Contents of a byte
Each transmitted sign begins with a start bit.
Subsequently, 8 databits are transmitted. Each sign is
given via a parity bit set at "1" when there is an even
parity (i.e. an even number of binary 1's in the 8
databits and parity bits together). The sign ends with
a stop bit and thus consists of a total of 11 bits.
Start 0 1 2 3 4 5 6 7 Even Stop
bit Parity bit
Telegram length (LGE)
The telegram length is the number of databytes plus
address byte ADR plus data control byte BCC.
Telegrams with 4 databytes have a length of:
LGE = 4 + 1 + 1 = 6 bytes
Telegrams with 12 databytes have a length of:
LGE = 12 + 1 + 1 = 14 bytes
Serial communication
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