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
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).
Coil
number
Description
Signal
direction
1–16
Frequency converter control word.
Master to slave
17–32
Frequency converter speed or
setpoint reference range 0x0–0xFFFF
(-200% ... ~200%).
Master to slave
33–48
Frequency converter status word (see
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 3.34 Coil Descriptions
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 freq.
No freeze freq.
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
Set up msb
16
No reversing
Reversing
Table 3.35 Frequency Converter Control Word (FC Profile)
System Integration
VLT
®
Refrigeration Drive FC 103
80
Danfoss A/S © 08/2015 All rights reserved.
MG16G202
3
3
Содержание VLT FC 103
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