Telegram Length (Lge); Frequency Converter Address (Adr); Data Control Byte (Bcc); The Data Field - Danfoss VLT Micro Drive FC 51 Design Manual

RS485 Installation and Set-...

8.4.3 Telegram Length (LGE)

The telegram length is the number of data bytes plus the
address byte ADR and the data control byte BCC.
4 data bytes
12 data bytes
Telegrams containing texts
Table 8.4 Length of Telegrams
1) The 10 is the fixed characters, while the n is variable (depending
on the length of the text).

8.4.4 Frequency Converter Address (ADR)

Address format 1–126
•
Bit 7 = 1 (address format 1–126 active).
•
Bit 0–6 = frequency converter address 1–126.

8.4.6 The Data Field

8 8
The structure of data blocks depends on the type of telegram. There are 3 telegram types, and the type applies for both
control telegrams (master⇒slave) and response telegrams (slave⇒master).
The 3 types of telegram are:
•
Process block (PCD).
•
Parameter block.
•
Text block.
Process block (PCD)
The PCD is made up of a data block of 4 bytes (2 words) and contains:
•
Control word and reference value (from master to slave).
•
Status word and present output frequency (from slave to master).
STX LGE
Illustration 8.6 Process Block
Parameter block
The parameter block is used to transfer parameters between master and slave. The data block is made up of 12 bytes (6
words) and also contains the process block.
STX LGE
Illustration 8.7 Parameter Block
68
®
VLT
LGE=4+1+1=6 bytes
LGE=12+1+1=14 bytes
10 1) +n bytes
ADR PCD1
ADR PKE IND
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Micro Drive FC 51
•
Bit 0–6 = 0 broadcast.
The slave returns the address byte unchanged to the
master in the response telegram.

8.4.5 Data Control Byte (BCC)

The checksum is calculated as an XOR-function. Before the
first byte in the telegram is received, the calculated
checksum is 0.
PWE PWE
high low
PCD2
PCD1 PCD2
BCC
BCC
MG02K402