Translation From Modbus Rtu Protocol To Fc Protocol; Pcd Mapping - Danfoss VLT 5000 Instruction Manual

Translation Refer to Serial Communication for FC
Protocol in the VLT 6000 Operating
from
Instructions for details on the Danfoss FC
Modbus RTU
protocol used for Modbus RTU serial
Protocol to
communication within the VLT 6000
FC Protocol
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)
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
be cleared by the Modbus master after
reading/writing text.
PWE PWE
PWE PWE PWE
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.
16
.
DECIMAL
/PWE /PWE
/PWE /PWE /PWE
HIGh HIGh HIGh HIGh HIGh LOW LOW LOW LOW LOW
Control packet
(master → slave)
Reply packet
(slave → master)
PCD PCD PCD PCD PCD /PCD /PCD /PCD /PCD /PCD
1 1 1 1 1
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
). IND must truncated.
HEX
PCD
1
Control word
(Coils 1 – 16)
DEC
Status word
(Coils 33 – 48)
DEC

PCD Mapping

MG.10.P2.22 - VLT is a registered Danfoss trademark
2 2 2 2 2
PCD
2
Reference value
(Coils 17 – 32)
DEC
Given output frequency
(Coils 49 – 64)
DEC