Odometer programming data parsing vehicle maintenance

Odometer programming data parsing vehicle maintenance 2008-01-09 15:49:43 Read 71 Comments 0 Font Size: medium and small
Today we analyze A car dashboard mileage most common data encoding, this encoding algorithm is designed to solve the number of read-write memory and designed. Using this algorithm models include: Most Audi, Volkswagen, Mercedes, BMW, and a small portion of the domestic models, such as Chery. Other models and a considerable part of the evolution of mileage from this algorithm is an algorithm or improvement comes.

Before analyzing this algorithm I first talk about the relationship between the data recorded in the form of two questions:

First, the positive anti-code code

Record data memory we generally use hexadecimal codes are recording methods, such as the 12345 (decimal) is recorded as: 3039 (hex).

But in the car dashboard we'll see another recording: Hex anti-code, such as the 12345 (decimal) is recorded as: CFC6 (hex inverted).

Positive anti-code and then the code how to convert it? We look at the hexadecimal calculation: CFC6 = FFFF-3039;

In fact, we can also use another, more straightforward conversion, just press table controls were one pair of bit conversion can be:

N code: 0 1 2 3 4 5 6 7 8 9 A B C D E F

Anti-code: F E D C B A 9 ​​8 7 6 5 4 3 2 1 0

Second, the problem of low and high data

Due to differences in CPU design and memory design, for the same time a 16-bit hexadecimal number of records may have high or low the previous design differences last.

The data 3039 (hex), some instruments will be recorded as follows: 3930.

Before the transfer table we must clarify our instrument is that a data recording mode, in which there are four possibilities, namely: positive code + high front and low positive code + front, anti-code + MSB first, anti-code + LSB first.

Here we begin to enter our subject today, we talk about mileage algorithms.

If we see this data in the data stored in the instrument: 3,039,303,930,393,039 3,039,303,930,383,038;

A very similar set of values, together (there may be 8 group, but also some 16 groups), this is what we want to mileage data.

Now we assume that the problem of high and low positive and negative data and code has been resolved, the data have been unified into positive yards, the previous high, and only eight sets of data in the discussion, we look at a few examples:

1KM: 0001 0000 0000 0000 0000 0000 0000 0000

2KM: 0001 0001 0000 0000 0000 0000 0000 0000

3KM: 0001 0001 0001 0000 0000 0000 0000 0000

8KM: 0001 0001 0001 0001 0001 0001 0001 0001

9KM: 0002 0001 0001 0001 0001 0001 0001 0001

10KM: 0002 0002 0001 0001 0001 0001 0001 0001

We soon see that the result is to put all the mileage data are combined, but most of the models are run every two kilometers of recording time data, and this time we came to the data should be multiplied by 2 only is the actual number of miles, as the data are then: 2KM, 4KM, 6KM, 16KM, 18KM, 20KM.

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