0
1
3
2
4
5
6
7
195NA036.10
Start
bit
Even Stop
Parity bit
Illustration 3.27
3.6.3 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
195NA099.10
Illustration 3.28 Telegram
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
VLT address (ADR)
Two different address formats are used:
1. Siemens USS protocol address format:
Illustration 3.29 Address Format
Bit 7 = 0
Bit 6 is not used
Bit 5 = 1: Broadcast, address bits (0-4) are not used
Bit 5 = 0: No Broadcast
Bits 0-4 = VLT address 1-31
2. Danfoss format:
Illustration 3.30 Address Format
Bit 7 = 1
Bits 0-6 = VLT address 1-127 (0 = Broadcast)
Data control byte (BCC)
The data control byte can best be explained by means of
an example: Before the first sign of the telegram is
received, BCC = 0.
Illustration 3.31
After the first sign has been received:
BCC
NEW
= BCC
OLD
EXOR "first byte"
(EXOR = exclusive-or gate)
BCC
OLD
= 0 0 0 0 0 0 0 0
EXOR
"first byte" = 0 0 0 0 0 0 1 0 (02H)
BCC
NEW
= 0 0 0 0 0 0 1 0
Each additional, subsequent byte is gated by
BCC
OLD
EXOR and gives a new BCC
NEW
, e.g.:
BCC
OLD
= 0 0 0 0 0 0 1 0
EXOR
"second byte" = 1 1 0 1 0 1 1 0 (D6H)
BCC
NEW
= 1 1 0 1 0 1 0 0
The result after the last received sign is BCC.
3.6.4 Databytes
The block of databytes is divided into two smaller blocks:
1.
Parameter bytes used for transferred parameters
between master and slave
2.
Process bytes, covering
-
Control word and reference value (from
master to slave)
-
Status word and present output
frequency (from slave to master)
This structure applies to both the control telegram (master
⇒
slave) and the reply telegram (slave
⇒
master).
Illustration 3.32
There are two types of telegrams:
Programming
VLT
®
DriveMotor FCM Series
MG03BA02 - VLT
®
is a registered Danfoss trademark
61
3
3
Summary of Contents for VLT Brook Crompton Motor FCM 300
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