Danfoss VLT AutomationDrive FC 360, Design Manual

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5.8.6 Data Field
The data field is constructed using sets of 2 hexadecimal
digits, in the range of 00 to FF hexadecimal. These are
made up of one RTU character. The data field of messages
sent from a master to slave device contains additional
information which the slave must use to take the action
defined by the function code. This can include items such
as coil or register addresses, the quantity of items to be
handled, and the count of actual data bytes in the field.
5.8.7 CRC Check Field
Messages include an error-checking field, operating based
on a cyclical redundancy check (CRC) method. The CRC
field checks the contents of the entire message. It is
applied regardless of any parity check method used for the
individual characters of the message. The CRC value is
calculated by the transmitting device, which appends the
CRC as the last field in the message. The receiving device
recalculates a CRC during receipt of the message and
compares the calculated value to the actual value received
in the CRC field. If the 2 values are unequal, a bus time-out
results. The error-checking field contains a 16-bit binary
value implemented as 2 8-bit bytes. When this is done, the
low-order byte of the field is appended first, followed by
the high-order byte. The CRC high-order byte is the last
byte sent in the message.
5.8.8 Coil Register Addressing
In Modbus, all data is organised in coils and holding
registers. Coils hold a single bit, whereas holding registers
hold a 2-byte word (that is 16 bits). All data addresses in
Modbus messages are referenced to 0. The first occurrence
of a data item is addressed as item number 0. For
example: The coil known as ‘coil 1’ in a programmable
controller is addressed as coil 0000 in the data address
field of a Modbus message. Coil 127 decimal is addressed
as coil 007Ehex (126 decimal).
Holding register 40001 is addressed as register 0000 in the
data address field of the message. The function code field
already specifies a ‘holding register’ operation. Therefore,
the ‘4XXXX’ reference is implicit. Holding register 40108 is
addressed as register 006Bhex (107 decimal).
Coil
Number Description Signal Direction
1-16 Frequency converter control word
(see
Table 5.16 )
Master to slave
17-32 Frequency converter speed or set-
point reference Range 0x0–0xFFFF
(-200% ... ~200%) Master to slave
33-48 Frequency converter status word
(see
Table 5.17 )
Slave to master
49-64 Open loop mode: Frequency
converter output frequency
Closed loop mode: Frequency
converter feedback signal Slave to master
65 Parameter write control (master to
slave) Master to slave
0
= Parameter changes are written
to the RAM of the frequency
converter
1
= Parameter changes are written
to the RAM and EEPROM of the
frequency converter.
66-65536 Reserved
Table 5.15 Coil Register
Coil 0 1
01 Preset reference LSB
02 Preset reference MSB
03 DC brake No DC brake
04 Coast stop No coast stop
05 Quick stop No quick stop
06 Freeze frequency No freeze frequency
07 Ramp stop Start
08 No reset Reset
09 No jog Jog
10 Ramp 1 Ramp 2
11 Data not valid Data valid
12 Relay 1 off Relay 1 on
13 Relay 2 off Relay 2 on
14 Set up LSB
15
16
No reversing Reversing
Table 5.16 Frequency Converter Control Word (FC Profile)
RS485 Installation and Set-... Design Guide
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