VLT
®
6000 HVAC
MG.60.B1.02 - VLT is a registered Danfoss trademark
122
- - - - - -
- - - - - -
Master
telegram
Slave
telegram
Pause
time
Response-
time
Pause
time
Each transferred character begins with a start bit.
Subsequently, 8 data-bits are transferred, corre-
sponding to one byte. Each character is secured via a
parity bit 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 bite
and thus consists of a total of 11 bits.
Start
0
1
2
3
4
5
6
7
Even Stop
bit
Parity bit
■
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).
STX
LGE
ADR
Data
BCC
Telegram times
The speed of communication between a master and a
slave depends on the baud rate. The baud rate of the
VLT 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.
Pause time, min.:
2 characters
Response time, min.:
2 characters
Response time, max.:
20 msec.
The time between individual characters in a telegram
is not to exceed 2 characters and the telegram must
be completed within 1.5 times the rated telegram
time.
If the baudrate is 9600 kbaud and the telegram
length is 16 baud, the telegram must be completed
within 27.5 msec.
STX
LGE
ADR
DATA
BCC
= Time between characters
Telegram length (LGE)
The telegram length is the number of data bytes plus
address byte ADR plus data control byte BCC.
Telegrams with 4 data bytes have a length of:
LGE = 4 + 1 + 1 = 6 bytes
Telegrams with 12 data bytes have a length of:
LGE = 12 + 1 + 1 = 14 bytes
Telegrams that contain text have a length of 10+n
bytes. 10 is the fixed characters, while 'n' is variable
(depending on the length of the text).
VLT frequency converter address (ADR)
Two different address formats are used, in which the
address range of the VLT frequency converter is either
from 1-31 or from 1-126.
1. Address format 1-31
The byte for this address range has the following
profile:
7
6
5
4
3
2
1
0
0
0
0
0
0
Bit 7 = 0 (address format 1-31 active)
Bit 6 is not used
Bit 5 = 1: Broadcast, address bits (0-4), not used
Bit 5 = 0: No Broadcast
Bit 0-4 = VLT frequency converter address 1-31
