Frequency Converter Address (Adr); Data Control Byte (Bcc); The Data Field - Danfoss VLT FC51 Design Manual

RS-485 Installation and Set...

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
Bit 0-6=0 Broadcast
The follower returns the address byte unchanged to the
master in the response telegram.

8.4.6 The Data Field

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⇒follower) and response telegrams (follower⇒master).
The 3 types of telegram are:
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 follower)
8 8
•
Status word and present output frequency (from follower to master)
STX LGE
Illustration 8.6 Process Block
Parameter block
The parameter block is used to transfer parameters between master and follower. The data block is made up of 12 bytes (6
words) and also contains the process block.
STX LGE
Illustration 8.7 Parameter Block
Text block
The text block is used to read or write texts via the data block.
STX LGE
Illustration 8.8 Text Block
68
VLT
ADR PCD1
ADR PKE IND
ADR PKE IND Ch1
®
Micro Drive FC 51 Design Guide

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
Ch2 Chn
MG02K302 - Rev. 2013-12-03
PCD2
PCD1 PCD2
PCD1 PCD2
BCC
BCC
BCC