JUMO mTRON T Manual page 40

3 Modbus protocol description
Example
In this example, the value of analog variable 1 is to be read out at address 0x1071 of the central
processing unit. The value here is to be 1234567.89 (0x4132D687E3D70A3D in the IEEE 754
format).
Data request:
01
Slave
Response (values in the Modbus double format):
01
Slave
NOTE!
The order of the bytes depends on how the double values are saved in the respective appli-
cation. The bytes may have to be changed over in the interface program accordingly.
3.7.4 Strings (texts)
Strings are transmitted in the ASCII format.
NOTE!
To mark the end, the last character to be transmitted must always be a "\0" (ASCII code
0x00). The subsequent characters have no meaning.
Since texts are transmitted word by word (16 bit), 0x00 is also added to the end for an uneven
number of characters (incl. "\0").
The maximum lengths for strings specified in the address tables contain the final "\0". This
means, in the case of "char 11", the text can consist of max. 10 readable characters.
 Chapter 7 "Modbus address tables", page 77
Example
Request the text of address 0x13F1; the string "test" (ASCII code: 0x54, 0x65, 0x73, 0x74,
0x00) is under this address.
Request: 010313F100027E11 (CRC16 = 117E)
Response: 010304546573740000AAB5B6 (CRC16 = B6B5)
NOTE!
The value (here: AA) before the CRC sum (here: B5B6) is not considered, since it follows the
end marker "\0".
40
03 10 71
Function Address
of the 1st word
03 08
Function Bytes
read
00 04
Number of
words
41 32 D6 87
Double value
D2 10
CRC
E3 D7 0A 3D CD A4
CRC