Serial Data Interface; Telegram Format; Data Format - Danfoss VLT 3000 Series Product Manual

Serial data interface

Group 5..

Data format

Group description
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
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

Telegram format

®
MG.30.A7.02 - VLT is a registered Danfoss trademark
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.
®
frequency
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.
®
Continued...
73