Operating Manual
ARS31(Pro)-UMB
G. Lufft Mess- und Regeltechnik GmbH, Fellbach, Germany
25
The freezing temperature is
–18.8°C.
Correct data transmission can be checked with the aid of the checksum (EAFFh).
Important:
Little endian (Intel, lowbyte first) applies when transmitting word and float
variables of such as, for example, addresses or the CRC. This means first the LowByte,
then the HighByte.
7.1.5 CRC calculation
The CRC is calculated in accordance with the following rules:
Standard:
CRC-CCITT
Polynomial: 1021h = x
16
+ x
12
+ x
5
+ 1 (LSB first mode)
Start value: FFFFh
(Attention: Contrary to earlier Lufft protocols, the start value for CRC calculations is not 0h
but rather FFFFh in accordance with CCITT)
Further information is available in the description of a CRC calculation in UMB Protocol.
7.2 ASCII protocol
Easy communication with devices is provided by using the ASCII protocol.
ASCII protocol serves exclusively for online data requests and is not secured by a CRC.
The device does not respond to incomprehensible ASCII commands.
Using ASCII protocol, the measurements can be polled in a simple, insecure manner with
the aid of a terminal program. However, the sensor can only be configured by way of the
binary protocol. The output format is fixed and not user-configurable. You can find an exact
description in the document Communication Protocol for Meteorological Sensors.
After the HyperTerminal has started, select File -> Properties
–> Settings -> ASCII
Configuration. Enter 1 ms for the character delay.
7.2.1 Construction
ASCII commands are introduced by the character ‘&’ and ended with the character CR
(0Dh). There is always a blank space (20h) between the individual blocks; this is
represented by an underscore ‘_’. Characters which represent an ASCII value are in
simple inverted commas.
7.2.2 Example of an ASCII request
If, for example, you want to request the current freezing temperature of a road sensor with
device ID (serial number) 0001 from a PC, this is done as follows:
A measurement of a specific channel is requested wit
h command “M”.
Request:
‘&’_<ID>
5
_’M’_<channel>
5
CR
Response:
‘$’_<ID>
5
_’M’_<channel>
5
_<value>
5
CR
<ID>
5
Device address (5-digit decimal with leading zeros)
<channel>
5
Gives the channel number (5-digit decimal with leading zeros)
<value>
5
Measurement (5-digit decimal with leading zeros); a standardized
measurement from 0
– 65520d. 65521d – 65535d define various error codes
Example:
Request: & 16385 M 00151
This request polls channel 151 of the device with the address 4001h.
Response: $ 16385 M 00151 62899
With the standardization for the freezing temperature the following calculation then results:
62899d
corresponds to -40+(0+40)*62899 / 65520 = -1.6 °C
