The Data Field - Danfoss VLT Compressor Drive CDS 803 Design Manual

RS485 Installation and Set-...

7.4.6 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⇒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 ADR
Illustration 7.6 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 ADR
Illustration 7.7 Parameter Block
Text block
The text block is used to read or write texts via the data block.
STX LGE ADR PKE
Illustration 7.8 Text Block
MG18N202
Design Guide
PCD1
PWE
PKE IND
high
IND Ch1 Ch2
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PCD2
PWE
PCD1
low
Chn PCD1
BCC
PCD2 BCC
PCD2 BCC
53
7 7