Operating Manual
ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany
23
7 Communication
Communication takes place with the ARS31PRO-UMB/ARS31-UMB over a 2-wire half-
duplex RS485 interface with the aid of the ISOCON-UMB. The bus is not terminated with a
resistor due to dissipation in the sensor. The use of PC software from Lufft for purposes of
maintenance and diagnosis makes an RS485-RS232 or RS485-USB converter
superfluous.
The protocol is based on meteorological sensor communications protocol. This contains
bus-compatible binary protocol which requires a strict master-slave principle and is
enabled on delivery. The sensor is a slave and only responds to requests. AN ASCII
protocol is available for rudimentary measurement polling only.
Depending on the device configuration, the calculated freezing point can be requested in
binary or ASCII protocol.
7.1 Binary protocol
This operating manual only includes one example of an online data request. Please refer
to the current version of the document
Communications Protocol for Meteorological
Sensors
(UMB protocol)
for details of the mode of operation.
7.1.1 Framing
The data frame is constructed as follows:
1
2
3 - 4
5 - 6
7
8
9
10
11 ... (8 + len)
optional
9 + len
10 + len
11 + len
12 + len
SOH
<ver>
<to>
<from>
<len>
STX
<cmd> <verc>
<payload>
ETX
<cs>
EOT
SOH
Control character for the start of a frame (01h) 1 byte
<ver>
Header version number, e.g.: V 1.0
<ver> = 10h = 16d; 1 byte
<to>
Receiver address, 2 bytes
<from>
Sender address, 2 bytes
<len>
Number of data bytes between STX and ETX; 1 byte
STX
Control character for the start of payload data transmission (02h); 1 byte
<cmd>
Command; 1 byte
<verc>
Version number of the command; 1 byte
<payload> Data bytes; 0
– 210 bytes
ETX
Control character for the end of payload data transmission (03h); 1 byte
<cs>
Checksum, 16 bit CRC; 2 bytes
EOT
Control character for the end of the frame (04h); 1 byte
Control character: SOH (01h), STX (02h), ETX (03h), EOT (04h).
7.1.2 Addressing of class and device ID
Addressing takes place using a 16 bit address. This is divided into sensor class ID and
device ID.
