VLT
®
Series 3500
85
Group 5 -- Serial Data Interface
The RS 485 serial bus (terminals 68 and 69) allows the
reading and setting of the drive’s parameters, as well as
transmitting reference and control commands to it.
The serial bus can be used by up to 31 drives per master
without using a repeater. If 3 repeaters are used, up to 99
drives can be connected to one master.
Danfoss can provide a serial communication program “VLS
Dialog”, which allows an IBM compatible personal com-
puter (PC) to communicate with VLT drives over an RS 485
serial interface. This program allows controlling the drive(s)
remotely through the computer without the need for any ad-
ditional programming. Contact Danfoss literature depart-
ment for information.
It is important to connect and terminate the serial bus with
the correct impedance to avoid any reflections which may
disturb the data transmission in the cable. Set the switches
03.1 and 03.2 in the “on” position in the last drive con-
nected to the serial bus.
The following information provides detailed specifications of
the serial communications format for those who wish to
customize their own serial communications software. Com-
munication takes place by means of s special protocol.
The data format consists of 10 bits; one start bit (logical 0),
eight data bits and one stop bit (logical 1). There is no par-
ity check. Set the speed of transmission in parameter 501
and the address of each unit in parameter 500.
Message (telegram) format (protocol)
The communication protocol consists of 22 ASCII charac-
ters. These characters make it possible to operate, set and
read parameters and to receive status feedback from the
drive.
Communication takes place as follows:
The master sends a message to the drive. Then the master
awaits a reply from the drive before sending a new mes-
sage. The reply to the master is a copy of the message sent
by the master, now containing any updated data values and
the status of the drive.
Telegram format
Data format
