VLT® 5000 Crane
Appendix
■
Serial Communication
■
Telegram Communication
Control and reply telegrams
Telegram communication in a master-slave system is
controlled by the master. A maximum of 31 slaves (VLT
5000 Crane) 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 sends control telegrams addressed to the
slaves and awaits reply telegrams from these. The
response time of the slaves is maximum of 50 ms.
A slave responds by sending a reply telegram
when it has received telegram with correct
STX, LGE, ADR and BCC..
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. Boradcast communication
is set up in the address format (ADR).
Content of a byte
Each transferred character begins with a start bit.
Subsequently, 8 data bits are transferred. Each
character is secured via a parity bit, which is set to
"1" when there is even parity (i.e. an even number
of binary 1
’
s in the 8 data bits and the parity bit
combined). A character ends with a stop bit, thus
consisting of a total of 11 bitsl.
■
Telegram Build-up
Each telegram begins with a start byte (STX) = 02
Hex, followed by a byte that states the telegram
length (LGE) and a byte that states the address of the
frequency converter (ADR). Then follows a number of
data bytes (variable, depending on telegram type). The
telegram ends with a data control byte (BCC).
Telegram timing
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
501
Baud rate
. 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 baud rate of 9600 baud, there must
be a minimum pause of 2.3 msec. After the master
MG.50.N4.02 - VLT is a registered Danfoss trademark
95
