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11.8.8 Coil Register Addressing
In Modbus, all data are organized in coils and holding registers. Coils hold a single bit, whereas holding registers hold a 2-byte word (i.e., 16 bits). All
data addresses in Modbus messages are referenced to zero. The first occurrence of a data item is addressed as item number zero. 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
Adjustable frequency drive control word (see table below)
Master to slave
17-32
Adjustable frequency driver speed or setpoint reference Range 0x0–0xFFFF (-200% ...
~200%)
Master to slave
33-48
Adjustable frequency drive status word (see table below)
Slave to master
49-64
Open-loop mode: adjustable frequency drive output frequency Closed-loop mode: Ad-
justable frequency drive 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 adjustable frequency
drive.
1 =
Parameter changes are written to the RAM and EEPROM of the adjust-
able frequency drive.
66-65536
Reserved
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
Adjustable frequency drive control word (FC profile)
Coil
0
1
33
Control not ready
Control ready
34
Adjustable frequency drive
not ready
Adjustable frequency drive
ready
35
Coasting stop
Safety closed
36
No alarm
Alarm
37
Not used
Not used
38
Not used
Not used
39
Not used
Not used
40
No warning
Warning
41
Not at reference
At reference
42
Hand mode
Auto mode
43
Out of freq. range
In frequency range
44
Stopped
Running
45
Not used
Not used
46
No voltage warning
Voltage warning
47
Not in current limit
Current limit
48
No thermal warning
Thermal warning
Adjustable frequency drive status word (FC profile)
FC 300 Design Guide
11 RS-485 Installation and Set-up
MG.33.BC.22 - VLT
®
is a registered Danfoss trademark
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