7.2 FC Protocol Overview
The adjustable frequency protocol, also referred to as adjustable frequency bus or standard bus, is the Danfoss standard serial communication bus. 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 individual slaves are selected by the master via an address character in the
message. 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 adjustable frequency drive. The adjustable frequency protocol supports different
message formats; a short format of 8 bytes for process data, and a long format of 16 bytes that also includes a parameter channel. A third message
format is used for texts.
7.2.1 VLT AQUA with Modbus RTU
The FC protocol provides access to the control word and bus reference of the adjustable frequency drive.
The control word allows the modbus master to control several important functions of the adjustable frequency drive:
•
Start
•
Stop of the adjustable frequency drive in various ways:
Coast stop
Quick stop
DC Brake stop
Normal (ramp) stop
•
Reset after a fault trip
•
Run at a variety of preset speeds
•
Run in reverse
•
Change of the active set-up
•
Control of the two relays built into the adjustable frequency drive
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 of the adjustable frequency drive when its internal PID controller is
used.
7 RS-485 Installation and Set-up
VLT
®
AQUA Drive Design Guide
7-4
MG.20.N5.22 - VLT
®
is a registered Danfoss trademark
7
Содержание vlt aqua
Страница 4: ...Contents VLT AQUA Drive Design Guide MG 20 N5 22 VLT is a registered Danfoss trademark...
Страница 168: ...5 How to Install VLT AQUA Drive Design Guide 5 50 MG 20 N5 22 VLT is a registered Danfoss trademark 5...
Страница 186: ...6 Application Examples VLT AQUA Drive Design Guide 6 10 MG 20 N5 22 VLT is a registered Danfoss trademark 6...