Data Field; Crc Check Field; Coil Register Addressing - Danfoss VLT AutomationDrive FC 360 Design Manual

RS485 Installation and Set-...

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

5 5
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).
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Design Guide
Coil
Number
1-16
17-32
33-48
49-64
65
66-65536
Table 5.15 Coil Register
Coil
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
Table 5.16 Frequency Converter Control Word (FC Profile)
Danfoss A/S © 09/2014 All rights reserved.
Description
Frequency converter control word
(see Table 5.16)
Frequency converter speed or set-
point reference Range 0x0–0xFFFF
(-200% ... ~200%)
Frequency converter status word
(see Table 5.17 )
Open loop mode: Frequency
converter output frequency
Closed loop mode: Frequency
converter feedback signal
Parameter write control (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.
Reserved
0 1
Preset reference LSB
Preset reference MSB
DC brake No DC brake
Coast stop No coast stop
Quick stop No quick stop
Freeze frequency No freeze frequency
Ramp stop Start
No reset Reset
No jog Jog
Ramp 1 Ramp 2
Data not valid Data valid
Relay 1 off Relay 1 on
Relay 2 off Relay 2 on
Set up LSB
No reversing Reversing
Signal Direction
Master to slave
Master to slave
Slave to master
Slave to master
Master to slave
MG06B402