implementation, 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 telegram.
8.8.8 Coil Register Addressing
8.8.8.1 Introduction
In Modbus, all data is organized 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 telegrams are referenced to 0. The 1
st
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 telegram. 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 telegram. The function code field already speci-
fies a holding register operation. Therefore, the 4XXXX reference is implicit. Holding register 40108 is addressed as register 006Bhex
(107 decimal).
8.8.8.2 Coil Register
Table 63: Coil Register
Coil number
Description
Signal direction
1–16
Drive control word.
Master to follower
17–32
Drive speed or setpoint reference range 0x0– 0xFFFF (-200% ... ~200%).
Master to follower
33–48
Drive status word.
Follower to master
49–64
Open-loop mode: Drive output frequency.
Closed-loop mode: Drive feedback signal.
Follower to master
65
Parameter write control (master to follower).
Master to follower
0 = Parameter changes are written to the RAM of the drive.
1 = Parameter changes are written to the RAM and EEPROM of the drive.
66–65536
Reserved.
–
8.8.8.3 Drive Control Word (FC Profile)
Table 64: Drive Control Word (FC Profile)
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
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RS485 Installation and Set-up
VLT® Flow Drive FC 111
Design Guide