Danfoss VLT Refrigeration Drive FC 103 Design Manual page 82

System Integration
chapter 3.9.10.10 Function Codes Supported by Modbus RTU
and chapter 3.9.10.11 Modbus Exception Codes.
3.9.10.6 Data Field
3 3
The data field is constructed using sets of 2 hexadecimal
digits, in the range of 00–FF hexadecimal. These are made
up of 1 RTU character. The data field of messages sent
from a master to a slave device contains extra information,
which the slave must use to act as 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.
3.9.10.7 CRC Check Field
Messages include an error-checking field, operating based
on a cyclic 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 transmitting
device calculates the CRC value and 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 timeout
occurs. 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.
3.9.10.8 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 (16 bits). All data addresses in Modbus
messages are referenced to zero. 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 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).
80
®
VLT Refrigeration Drive FC 103
Coil
number
1–16
17–32
33–48
49–64
65
66–
65536
Table 3.34 Coil Descriptions
Coil
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
Table 3.35 Frequency Converter Control Word (FC Profile)
Danfoss A/S © 08/2015 All rights reserved.
Description
Frequency converter control word.
Frequency converter speed or
setpoint reference range 0x0–0xFFFF
(-200% ... ~200%).
Frequency converter status word (see
Table 3.36).
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 freq. No freeze freq.
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
Set up msb
No reversing Reversing
Signal
direction
Master to slave
Master to slave
Slave to master
Slave to master
Master to slave
MG16G202