Fc Protocol Overview - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS-485 Installation and Set...
7.1.4 Frequency Converter Parameter
Settings for Modbus Communication
The following parameters apply to the RS-485 interface
(FC-port):
Parameter
8-30 Protocol
8-31 Address
8-32 Baud Rate
7 7
8-33 Parity / Stop
Bits
8-35 Minimum
Response Delay
8-36 Maximum
Response Delay
8-37 Maximum
Inter-char delay
Table 7.2
7.1.5 EMC Precautions
To achieve interference-free operation of the RS-485
network, Danfoss recommends the following EMC
precautions.
Relevant national and local regulations, for example
regarding protective earth connection, must be observed.
To avoid coupling of high frequency noise between the
cables, the RS-485 communication cable must be kept
away from motor and brake resistor cables. Normally a
distance of 200 mm (8 inches) is sufficient, but Danfoss
recommends keeping the greatest possible distance
between the cables. Especially where cables run in parallel
over long distances. When crossing is unavoidable, the
RS-485 cable must cross motor and brake resistor cables at
an angle of 90°.
78
®
VLT
Function
Select the application protocol to run on
the RS-485 interface
Set the node address.
NOTE
The address range depends on the
protocol selected in 8-30 Protocol
Set the baud rate.
NOTE
The default baud rate depends on the
protocol selected in 8-30 Protocol
Set the parity and number of stop bits.
NOTE
The default selection depends on the
protocol selected in 8-30 Protocol
Specify a minimum delay time between
receiving a request and transmitting a
response. This function is for overcoming
modem turnaround delays.
Specify a maximum delay time between
transmitting a request and receiving a
response.
If transmission is interrupted, specify a
maximum delay time between two received
bytes to ensure time-out.
MG18C402 - VLT
HVAC Basic Drive Design Guide

7.2 FC Protocol Overview

The FC protocol, also referred to as FC bus or Standard
bus, is the Danfoss standard fieldbus. It defines an access
technique according to the master-slave principle for
communications via a serial bus.
One master and a maximum of 126 slaves can be
connected to the bus. The master selects the individual
slaves via an address character in the telegram. A slave
itself can never transmit without first being requested to
do so, and direct message transfer between the individual
slaves is not possible. Communications occur in the half-
duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS-485, thus utilizing the RS-485 port
built into the frequency converter. The FC protocol
supports different telegram formats:
•
A short format of 8 bytes for process data.
•
A long format of 16 bytes that also includes a
parameter channel.
•
A format used for texts.
7.2.1 FC with Modbus RTU
The FC protocol provides access to the Control Word and
Bus Reference of the frequency converter.
The Control Word allows the Modbus master to control
several important functions of the frequency converter.
•
Start
•
Stop of the frequency converter in various ways:
•
•
•
•
•
Reset after a fault trip
•
Run at various preset speeds
•
Run in reverse
•
Change of the active set-up
•
Control of the 2 relays built into the frequency
converter
The Bus Reference is commonly used for speed control. It
is also possible to access the parameters, read their values,
and where possible, write values to them. This permits a
range of control options, including controlling the setpoint
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Coast stop
Quick stop
DC Brake stop
Normal (ramp) stop