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Protocol description
Character strings (texts)
Character strings (texts) are transmitted in the ASCII format.
To mark the end, the last character to be transmitted can be a "\0" (ASCII code 0x00).
Characters after this mark are without significance.
The address tables show the max. possible number of characters in a data type, e.g.
"TEXT24" (24 characters). When an end mark is used, then only 23 readable characters
are available for the text in this example.
If no end mark is used, the use of the maximum number of characters (e.g. TEXT8 =
8 characters) indicated in the data type is required. This prevents characters still
contained in the memory from being appended to the text.
Knowing that the transmission of texts takes place word by word (16 bits), 0x00 is
additionally appended where an odd number of characters is used (incl. "\0").
Example for data type TEXT4
Read the text (here: "AbC ") under address 0x0067 (a max. of 4 characters can be saved)
ASCII code for "AbC " (with one space at the end):
0x41, 0x62, 0x43, 0x20
Request: 01 03 0067 0002 (+ 2 byte CRC16)
Slave address = 01
Function = 03, i.e. read n words
Address = 0067
N umber of words to be read = 0002, because of the maximum of 4
characters
Response: 01 03 04 41 62 43 20 (+ 2 byte CRC16)
Slave address = 01
Function = 03, i.e. read n words
Number of bytes read = 04
Variant:
ASCII code for "Ab" (without a space at the end):
0x41, 0x62, 0x00
ASCII 0x00 ("\0") marks the end of the character string.
During transmission, 0x00 is additionally appended to obtain an even number of
characters.
Response in this case: 01 03 04 41 62 00 00 (+ 2 byte CRC16)
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