Lufft CHM 8k, User Manual, Page: 38 / 72

Operating Manual CHM 8k
R1.7 / 01-2020
Communication via RS485 & Ethernet 38
transmission takes about 16 seconds. The automatic output of the raw data telegram is restricted to
specific logging time / Baud rate combinations, as set out in Table 11 below.
Baud rate no. Baud rate [bit/s] Logging time interval [dt(s)]
0 1,200
Not possible
1 2,400
Not possible
2 4,800
≥ 40 s
3 9,600
≥ 20 s
4 19,200
≥ 10 s
5 38,400
≥ 5 s
6 57,600
No further restrictions
7 115,200
No further restrictions
Table 11 Baud rate
– logging time restrictions.
Table 12
describes the structure of the additional data of the raw data telegram.
Byte Value Description
0-238
Exactly as in the extended data telegram (for 3 cloud layers)
239 <CR>
0D HEX
240 <LF> 0A HEX
241-(eeee-5) Raw data in ASCII format (UUencode)
eeee-4
eeee-3
**
Checksum (
two’s complement of the sum of bytes 0 to eeee,
excluding bytes eeee-4 and eeee-3, expressed in Hex code)
eeee-2 <CR> 0D HEX
eeee-1 <LF> 0A HEX
eeee <EOT> 04 HEX
Table 12 Raw data telegram format; * = any character.
The lines with the raw data have the following structure according to UUencode standard:
Line 1:
begin 644 YYYYMMDDhhmmss_[Location]_[Device ID].nc<CR><LF>
Line 2:
M********************************************************<CR><LF>
Line 3:
M********************************************************<CR><LF>
...
Line (n-2):
M********************************************************<CR><LF>
Line (n-1):
E************************************************* ***<CR><LF>
Line n:
end<CR><LF>
The * character indicates a UUencode ASCII character in the range HEX 21-60.
The "M" (HEX 4D) at the beginning of the data lines stands for the likewise UUencoded number of data
bytes in this line:
- 4D decoded corresponds to the number HEX 2D = 45 decimal.
According to 4/3 UUencode conversion, these 45 bytes are encoded into 60 (60 = 45/3 x 4) ASCII
characters, which follow "M". The last line is an exception, as the last bytes, which are generally less than
45, are encoded.
The above example shows "E" (HEX 45, decoded HEX 25 = 37 decimal), hence a further 37 bytes of raw
data follow. As a result of the 4/3-encoding, however, this becomes 52 ASCII characters (rounded up to
a multiple of 4 characters) (52 = (37/3 rounded) x 4).
The last line with "end" marks the completion of the UUencode data.