16
MG.10.P2.22 - VLT is a registered Danfoss trademark
Translation
from
Modbus RTU
Protocol to
FC Protocol
Refer to
Serial Communication for FC
Protocol
in the
VLT 6000 Operating
Instructions
for details on the Danfoss FC
protocol used for Modbus RTU serial
communication within the VLT 6000
Adjustable Frequency Drive.
Parameter Block
PKE
PKE
PKE
PKE
PKE
PKE contains AK with the parameter
commands and replies, and PNU with the
parameter number. The AK value is
determined by the Modbus function code.
Coil 65 decimal determines whether data
written to the drive are stored in EEPROM
and RAM (coil 65 = 1) or just RAM (coil 65 =
0). PNU is translated from the register address
contained in the Modbus read/write
message. The parameter number is
translated to Modbus as (10 x parameter
number)
DECIMAL
.
IND
IND
IND
IND
IND
IND contains the index. The index is used,
together with the parameter number, for
read/write access. Index has 2 bytes – a low
byte and a high byte. However, only the low
byte is used for indexing. The high byte is
used for reading and writing text. IND is set
by a register in Modbus (40001
HEX
). IND must
be cleared by the Modbus master after
reading/writing text.
PWE
PWE
PWE
PWE
PWE
HIGh
HIGh
HIGh
HIGh
HIGh
/PWE
/PWE
/PWE
/PWE
/PWE
LOW
LOW
LOW
LOW
LOW
PWE contains the parameter value. The
parameter value block consists of 2 words (4
bytes). The value depends on the command
given (AK). PWE is zero filled on reads. On
writes, PWE is filled with the data field of the
Modbus write message.
PCD
1
PCD
2
Control packet
(master
→
slave)
Control word
(Coils 1 – 16)
DEC
Reference value
(Coils 17 – 32)
DEC
Reply packet
(slave
→
master)
Status word
(Coils 33 – 48)
DEC
Given output frequency
(Coils 49 – 64)
DEC
PCD
PCD
PCD
PCD
PCD
1
1
1
1
1
/PCD
/PCD
/PCD
/PCD
/PCD
2
2
2
2
2
PCD contains the process word block. The
parameter value block consists of 2 words (4
bytes). The process word block is divided into
two blocks of 16 bits and is stored in Modbus
as status coils. The mapping of the PCD is
shown below.
Process Block Updates
Upon every write to the PCD coils, the
process block is written to the drive and
returned from the drive. On parameter reads
and writes, the PCD is deactivated on
messages from the Modbus RTU option card
to the drive. The PCD coils are updated on
response messages from the drive to the
Modbus RTU option card.
Text Blocks
Parameters stored as text strings are
accessed the same as the other parameters
except PWE is replaced with the text block.
The maximum text block size is 20
characters. If a read request for a parameter
is for more characters than the parameter
stores, the response is space filled. If the read
request for a parameter is for less characters
than the parameter stores, the response is
truncated.
PCD Mapping
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