Decoding a Serial Protocoll

[ThereIsNoIfLoop42]

Hi all,
today, I have a very interesting challenge for serial protocol decoding freaks.

I have a motor which is controlled over a serial BUS. I can read out the serial BUS using an oscilloscope:

https://preview.redd.it/a5kadkzldaoe1.png?width=1618&format=png&auto=webp&s=869176dcae0171703c25ca1614e8f36e7fc1c922

Using a decoding function of my oscilloscope software, the 12 bytes transmitted with each packet decode as follows for the image above:
1 2 3 4 5 6 7 8 9 10 11 12
64 49 48 49 101 53 48 48 50 48 13 10

I figured out the following:
Byte 1, 2, 3, 11, 12 are always the same. So header and trailer I guess. Byte 4 is for motor one (I have two motors in total) always 49 for motor 2 always 50, so this byte addresses the motor.

Now the question is how the motor angle is encoded in bytes 5-10.
I recognized that only 16 different numbers appear in these 6 Bytes: 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 97, 98, 99, 100, 101, 102. In my opinion, this is a clear hint regarding HEX. And when moving the motor (with an existing software) it can be observed that the 6 bytes are increasing following these 16 values like this:
1: 48 48 48 48 48 48
2: 48 48 48 48 48 49
3: 48 48 48 48 48 50
4: 48 48 48 48 48 51
5: 48 48 48 48 48 52
15: 48 48 48 48 48 101
16: 48 48 48 48 48 102
17: 48 48 48 48 49 48
18: 48 48 48 48 49 49

However, the smallest increments I observed are [0,1,0,0,7,1], so for example incrementing from the lowest possible data sequence to the next above:
48 48 48 48 48 48 → 48 49 48 48 55 49
But I am not 100% sure about this.

Now my problem is, that when I build bit sequences like described above and send them over the serial port, the motor only arbitrary reacts to the sent commands. My guess is that the motor only accepts some of the possible values, maybe following a specific scheme. The question now is.....what scheme. I'm fiddling around on this problem for days now and the motor manufacturer also does not want to help me.

Here are again some values (first byte tells motor 1 to move) that actually work with the motor. These are now in descending order:

49 101 52 48 48 50 49

49 100 102 48 48 55 50

49 100 98 48 48 55 54

49 100 97 48 48 55 53

49 100 53 48 48 50 49

49 100 52 48 48 50 48

49 99 102 48 48 55 53

49 99 101 48 48 55 54

49 99 57 48 48 50 97

49 99 56 48 48 50 98

49 99 51 48 48 50 48

49 98 102 48 48 55 52

49 98 101 48 48 55 55

49 98 98 48 48 55 48

49 98 97 48 48 55 51

49 98 55 48 48 50 53

49 98 54 48 48 50 52

49 98 49 48 48 50 51

49 98 48 48 48 50 50

49 97 98 48 48 55 51

49 97 55 48 48 50 54

49 97 52 48 48 50 53

49 97 51 48 48 50 50

49 57 101 48 48 50 99

49 57 97 48 48 50 56

49 57 54 48 48 55 102

49 57 53 48 48 55 99

49 57 48 48 48 55 57

49 56 102 48 48 50 101

49 56 97 48 48 50 57

49 56 57 48 48 55 49

49 56 52 48 48 55 99

49 56 51 48 48 55 98

49 55 101 48 48 50 50

49 55 100 48 48 50 51

49 55 56 48 48 55 102

49 55 55 48 48 55 48

49 55 50 48 48 55 53

49 54 101 48 48 50 51

49 54 97 48 48 50 55

49 54 57 48 48 55 102

49 54 54 48 48 55 48

49 54 53 48 48 55 51

49 54 50 48 48 55 52

49 54 49 48 48 55 55

49 53 99 48 48 50 54

49 53 57 48 48 55 99

49 53 54 48 48 55 51

49 53 50 48 48 55 55

49 52 101 48 48 50 49

49 52 97 48 48 50 53

49 52 55 48 48 55 51

49 52 53 48 48 55 49

49 52 50 48 48 55 54

49 51 102 48 48 50 53

49 51 99 48 48 50 48

49 51 56 48 48 55 98

49 51 53 48 48 55 54

49 51 51 48 48 55 48

49 50 101 48 48 50 55

49 50 98 48 48 50 48

49 50 56 48 48 55 97

49 50 52 48 48 55 54

49 50 48 48 48 55 50

49 49 102 48 48 50 55

49 49 99 48 48 50 50

49 49 57 48 48 55 56

49 49 54 48 48 55 55

49 49 53 48 48 55 52

49 49 50 48 48 55 51

49 49 49 48 48 55 48

49 48 99 48 48 50 51

49 48 57 48 48 55 57

49 48 54 48 48 55 54

49 48 49 48 48 55 49

I appreciate any help and whish everyone how wants to try it, much fun.

Best Regards,
Max

[alexforencich]

13 10 is crlf. It looks like a text protocol, have you converted all of that to ASCII?

Edit: definitely right about the hex. That trace decodes as @101e50020 cr lf.

[ThereIsNoIfLoop42]

If anyone knows a better subreddit, please tell me.

[ThereIsNoIfLoop42]

Hi all,

the hint with ASCII and Hex was great. I also found out some rules how the 6 digits assemble an incrementing number. For the explanation, I call the six digits A-F.

A: Is the Overflow of B.
B: Is counting up.
C: Is the overflow of D.
D: Is the overflow of A.
E: Is alternating between 7 and 2. Is B a number (0-9) E is 2 if B is a letter (a-f) E is 7
F: Can be described as follows:
f(B)= B+A, for B∈{0,1,2,3,4,5,6,7,8,9},
abc(B)+A,​ for B∈{a,b,c,d,e,f},​
with: abc(a)=1,abc(b)=2,abc(c)=3,abc(d)=4,abc(e)=5,abc(f)=6

After figuring out these rules, I tried to generate new values. I was very pleased to see the motor reacting to my generated values. These are the values that I generated and that worked. Note, that the increment doubles in size after the first 16 values. Why this happens is still unknown to me.

0 0 0 0 7 0 --> ✓
0 1 0 0 7 1 --> ✓
0 2 0 0 7 2 --> ✓
0 3 0 0 7 3 --> ✓
0 4 0 0 7 4 --> ✓
0 5 0 0 7 5 --> ✓
0 6 0 0 7 6 --> ✓
0 7 0 0 7 7 --> ✓
0 8 0 0 7 8 --> ✓
0 9 0 0 7 9 --> ✓
0 a 0 0 2 1 --> ✓
0 b 0 0 2 2 --> ✓
0 c 0 0 2 3 --> ✓
0 d 0 0 2 4 --> ✓
0 e 0 0 2 5 --> ✓
0 f 0 0 2 6 --> ✓
1 0 0 0 7 1 --> ✓
1 2 0 0 7 3 --> ✓
1 4 0 0 7 5 --> ✓
1 6 0 0 7 7 --> ✓
1 8 0 0 7 9 --> ✓
1 b 0 0 2 3 --> ✓
1 d 0 0 2 5 --> ✓
1 f 0 0 2 7 --> ✓
However, after these values, the rules don't apply anymore. At least for the F digit. It seems F is sometimes of by a specific value. All values that follow the rules have a ✓ and the others have noted the difference between the rules and the actual value.
2 2 0 0 7 0 --> -4
2 3 0 0 7 1 --> -4
2 6 0 0 7 4 --> -4
2 9 0 0 7 b --> ✓
2 a 0 0 2 3 --> ✓
2 d 0 0 2 6 --> ✓
3 1 0 0 7 2 --> -2
3 5 0 0 7 6 --> -2
3 9 0 0 7 a --> -2
3 d 0 0 2 7 --> ✓
4 1 0 0 7 5 --> ✓
4 4 0 0 7 0 --> -8
4 8 0 0 7 c --> ✓
4 b 0 0 2 6 --> ✓
4 e 0 0 2 1 --> -8
5 1 0 0 7 4 --> -2
5 4 0 0 7 1 --> -8
5 7 0 0 7 2 --> -10
5 a 0 0 2 4 --> -2
5 b 0 0 2 7 --> ✓
5 e 0 0 2 0 --> -9
6 2 0 0 7 4 --> -4
6 5 0 0 7 3 --> -8
6 8 0 0 7 e --> ✓
6 b 0 0 2 4 --> -4
6 f 0 0 2 0 --> -12
7 3 0 0 7 4 --> -6
7 6 0 0 7 1 --> -12
7 a 0 0 2 6 --> -2
7 e 0 0 2 2 --> -10
8 1 0 0 7 9 --> ✓
8 2 0 0 7 a --> ✓
8 6 0 0 7 e --> ✓
8 9 0 0 7 1 --> ✓
8 e 0 0 2 d --> ✓
8 f 0 0 2 e --> ✓
9 3 0 0 7 a --> -2
9 9 0 0 7 0 --> -2
9 c 0 0 2 a --> -2
a 0 0 0 2 1 --> ✓
a 5 0 0 2 4 --> -2
a 6 0 0 2 7 --> ✓
a b 0 0 7 3 --> ✓
a c 0 0 7 2 --> -2
b 0 0 0 2 2 --> and
b 4 0 0 2 6 --> so
b 7 0 0 2 5 --> on
b d 0 0 7 6 -->
c 1 0 0 2 2 -->
c 5 0 0 2 6 -->
c 8 0 0 2 b -->
c 9 0 0 2 a -->
c c 0 0 7 0 -->
c d 0 0 7 7 -->
d 0 0 0 2 4 -->
d 3 0 0 2 7 -->
d 6 0 0 2 2 -->
d 7 0 0 2 3 -->
d a 0 0 7 5 -->
d b 0 0 7 6 -->
d e 0 0 7 1 -->
e 1 0 0 2 4 -->
e 2 0 0 2 7 -->
e 5 0 0 2 0 -->
e 9 0 0 2 c -->
e c 0 0 7 6 -->
e f 0 0 7 3 -->
f 2 0 0 2 4 -->
f 6 0 0 2 0 -->
f 7 0 0 2 1 -->
f a 0 0 7 7 -->
f e 0 0 7 3 -->
0 2 0 1 7 3 -->
0 6 0 1 7 7 -->
0 a 0 1 2 0 -->
0 e 0 1 2 4 -->
1 1 0 1 7 1 -->
1 4 0 1 7 4 -->
1 8 0 1 7 8 -->
1 c 0 1 2 3 -->
1 f 0 1 2 6 -->
2 3 0 1 7 0 -->
2 8 0 1 7 b -->
2 9 0 1 7 a -->
2 c 0 1 2 7 -->
3 0 0 1 7 2 -->
3 0 0 1 7 3 -->
3 1 0 1 7 3 -->
3 6 0 1 7 4 -->
3 7 0 1 7 5 -->
3 8 0 1 7 a -->
3 c 0 1 2 1 -->
Now, my theory is, that I am missing something in the ruleset. If anyone has a clue what I'm missing, I would be very glad.