VLT® 5000 Crane
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 baud rate is 9600 baud and the telegram
length is 16 characters, the telegram must be
completed within 27.5 msec.
T
elegram length (LGE)
The telegram length is the number of data bytes plus
the address byte ADR plus the data control byte BCC.
Telegrams with 4 data bytes have a length of:
LGE=4+1+1=6bytes
Telegrams with 12 data bytes have a length of:
LGE=12+1+1=14bytes
V
LT address (ADR)
Two different address formats are used, in which
the address range of the 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:
Bit 7 = 0 (address format 1-31 active)
Bit 6 is not used
Bit 5 = 1: Broadcast, address bits (0-4) are not used
Bit 5 = 0: No Broadcast
Bit 0-4 = Frequency converter address 1-31
2. Address format 1-126:
Thebyteforthe1-126addressrangehas
the following profile:
Bit 7 = 1 (address format 1-126 active)
Bit 0-6 = Frequency converter address 1-126
Bit 0-6 = 0 Broadcast
The slave sends the address byte back to the master
in the reply telegram in unchanged form.
E
xample
A telegram is sent to frequency converter address
22 using address format 1-31:
7 6 5 4 3 2 1 0
0 0 0 1 0 1 1 0
Data control byte (BCC)
The data control byte is the EXOR-sum of the entire
telegram. It is best explained by means of an example:
Before the first byte of the telegram is received, BCC is 0.
When the first byte has been received:
BCC
NEW
=BCC
OLD
EXOR "first byte"
(EXOR = exclusive-or gate)
BCC
OLD
=00000000
EXOR
1. byte =00000010(02H)
BCC
NEW
=00000010
Each subsequent byte gates with BCC
OLD
EXOR
and produces a new BCC
NEW
, e.g.:
BCC
OLD
=00000010
EXOR
2ndbyte =11010110(D6H)
BCC
NEW
=11010100
The result after the latest incoming byte is BCC.
■ Databytes
The build-up of data blocks depends on the type
of telegram. There are three types of telegram and
the telegram type applies to both control telegram
(master→slave) and reply telegram (slave→master).
The three types of telegrams are the following:
1. Parameter block, used for transferring parameters
between master and slave. The data block has 12
bytes 6 words and also contains the process block.
2. Process block, built up as a data block with
four bytes (2 words), covering:
- Control word and reference value (from
master to slave)
- Status word and present output frequency
(from slave to master)
MG.50.N4.02 - VLT is a registered Danfoss trademark
96
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