Danfoss VLT FCD 311 Design Manual page 95

Response time, max: 20 ms
The time between the individual characters in a tele-
gram may not exceed 2 characters and the telegram
must be completed within 1.5 x nominal telegram
time. At a baud rate of 9600 baud and a telegram
length of 16 bytes the telegram will be completed af-
ter 27.5 msec.
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 variable (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
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
The byte for address range 1 - 126 has the following
profile:
MG.04.A1.02 - VLT is a registered Danfoss trade mark
®
VLT FCD Series
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 with ad-
dress 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 gate)
BCS = 0 0 0 0 0 0 0 0
EXOR
1. byte = 0 0 0 0 0 0 1 0 (02H)
BCC = 0 0 0 0 0 0 1 0
Each subsequent byte gates with BCS EXOR and
produces a new BCC, e.g.:
BCS = 0 0 0 0 0 0 1 0
EXOR
2nd byte = 1 1 0 1 0 1 1 0 (D6H)
BCC = 1 1 0 1 0 1 0 0
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