73
MG.30.A7.02 - VLT
®
is a registered Danfoss trademark
Serial data interface
Group 5..
The serial bus communicates using RS
485 (terminals 68 and 69). It is possible to
read and set the parameters of the VLT
®
frequency converter, and to give it refer-
ence and control commands. The serial port
can be used by up to 31 VLT
®
frequency converters per master without us-
ing a repeater. If 3 repeaters are used,
up to 99 VLT
®
frequency converters can be
connec-ted to one master.
It is important to connect and terminate the
serial bus with the correct impedance to
avoid any reflections which may disturb the
cable’s data transmission.
This adjustment can take place by setting
the 03.1 and 03.2 switches in the “on” posi-
tion (see p. 148) in the last VLT
®
frequency
converter connected to the serial BUS.
Communication takes place by means of a
protocol specified by Danfoss.
The data format
consists of 10 bits: one
start bit (logically 0), eight data bits, and one
stop bit (logically 1). There is no parity
check. Set the baud rate (speed of trans-
mission) in parameter 501 and the ad-
dress of each unit in parameter 500.
Telegram format / protocol
The communication protocol for the VLT
®
3000 Series consists of a 22-byte telegram
using ASCII characters. These characters
make it possible to operate, set and read
parameters, and to receive status feed-
back from the VLT
®
frequency converter.
Communication takes place in the following
way: The master sends a telegram to a
VLT
®
frequency converter. Then the master
awaits a reply from that frequency con-
verter before sending a new message.
The reply to the master is a copy of the
telegram sent by the master, now
containing any updated data values and
the status of the VLT
®
frequency converter.
Data format
Telegram format
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Group description
