19 - 40
021774/07/14
6.1.1.2 Sensor data telegram
The Weather Station responds to the command "00TR2\r" with the sensor data telegram. The telegram
structure is given in the following table:
Position
Length
Example
Description
1
1
<STX> 0x02
Start of text characters.
2
10
##########
Serial number.
12
1
;
Semicolon.
13
5
##-##
HW version (e.g. 06-11).
18
1
;
Semicolon.
19
5
##.##
SW version (e.g. 01.00).
24
1
;
Semicolon.
25
6
####.#
Height of Weather Station referred to height above sea level in
metres, derived from the GPS data (Geoid Model).
31
1
*
Asterisk as separator for the checksum.
32
2
##
8-bit checksum in hexadecimal format (00
– FF). The checksum is
calculated from the exclusive OR link of all characters after STX to
the character before "*".
34
1
<ETX> 0x03
End of text characters.
35
1
<CR> 0x0D
Carriage return.
36
1
<LF> 0x0A
Line feed.
Table 3 : Sensor data telegram
6.2 Command interpreter MODBUS RTU
Once the command interpreter is selected the transmitted bytes are interpreted according to the
MODBUS specification (http://www.modbus.org/). Here, the weather station WSC11 is representing a
MODBUS Slave.
The data transmission is carried out in packages, so-called frames, of maximum 256 bytes. Each
package contains a 16bit CRC checksum (initial value: 0xffff).
Slave-Address
Function code
Data
CRC
1byte
1byte
0...252byte(s)
2bytes
CRC low-byte
CRC high-byte
Table 4 : MODBUS Frame
The following MODBUS functions are supported:
-
0x04 (Read Input Register).
-
0x03 (Read Holding Registers).
-
0x06 (Write Single Register).
-
0x10 (Write Multiple Registers).
The weather station WSC11 supports a write access for the slave-
address 0 (“Broadcast”).
All received MODBUS request are checked for validity before carrying out. In error case the weather
station responds with one of the following exceptions (
MODBUS Exception Responses).
