Telegram length (LGE)
The telegram length is the number of data bytes plus
the address byte ADR plus the data control byte BCC.
The length of telegrams with 4 data bytes is:
LGE = 4 + 1 + 1 = 6 bytes
The length of telegrams with 12 data bytes is:
LGE = 12 + 1 + 1 = 14 bytes
The length of telegrams containing texts is 10+n bytes.
10 represents the fixed characters, while the 'n' is var-
iable (depending on the length of the text).
Frequency converter address (ADR)
Two different address formats are used, with the fre-
quency converter's address range being either 1-31 or
1-126.
1. Address format 1-31
The byte for address range 1-31 has the following pro-
file:
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
The byte for address range 1 - 126 has 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 unchanged in
the response telegram to the master.
Example:
writing to frequency converter address 22 (16H) with
address format 1-31:
Data control byte (BCC)
The data control byte is explained in this example:
Before the first byte in the telegram is received, the
Calculated CheckSum (BCS) is 0.
When the
first byte (02H) has been received:
BCS = BCC EXOR “first byte”
(EXOR = exclusive-or)
BCS = 0 0 0 0 0 0 0 0 (00 H)
EXOR
1. byte
= 0 0 0 0 0 0 1 0 (02H)
BCC = 0 0 0 0 0 0 1 0 (02H)
Each subsequent byte gates with BCS EXOR and pro-
duces a new BCC, e.g.:
BCS = 0 0 0 0 0 0 1 0 (02H)
EXOR
2nd byte
= 1 1 0 1 0 1 1 0 (D6H)
BCC = 1 1 0 1 0 1 0 0 (D4H)
112 MG.27.E2.02 - VLT is a registered Danfoss trademark
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