Guru
Joined: 31/12/2012
Location: New ZealandPosts: 2492
| Posted: 11:42am 09 Aug 2020 |
from the above link:
"If the ROM does not follow the pattern 28-xx-xx-xx-xx-00-00-xx then the DS18B20 sensor is a clone [5]."
and
"References
5. Own investigations 2019, unpublished."
the only statement about the content of the ROM made by the DS18B20 datasheet is:
"The least significant 8 bits of the ROM code contain the DS18B20’s 1-Wire family code: 28h. The next 48 bits contain a unique serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is calculated from the first 56 bits of the ROM code."
based upon the DS18B20 datasheet, and without further input directly from Maxim, i'd find it hard to accept as gospel the "00 00" assertion; Maxim and/or DS could have in the past released any (large or small) number of DS18B20 with non-zero values in the 6th and 7th byte of the ROM.
i also have doubts about the forensic usefulness of the default contents of EEPROM - these values could innocently be changed by Maxim during manufacture and testing, during sample testing post-manufacturing, or by anyone in the supply chain who may have wished to test devices they handled. Maxim may have a number of plants capable of manufacturing DS18B20, and different plants could use their own individual testing and calibration routines that leave the EEPROM contents in set to a pattern identified as 'fake' .
apart from abnormal behaviour (including inaccuracy), the only sure way to identify a non-maxim part is to split the case open and examine the silicon die.
cheers,
rob :-)
Edited 2020-08-09 21:47 by robert.rozee