[En-Nut-Discussion] AD conversion resolution?

[Arius - Rick Collins]

At 06:11 AM 12/16/2005, you wrote:
>Been investigating it a bit further based on the same data and I found 
>that the two major gaps in my data show a "funny" symmetry:
>255 - 304 and 719 - 768 both have a gap of 49 and 255+768 = 304+719 = 1023.
>Been investigating the gaps in the data a bit more and to my surprise, 
>this symmetry occurs throughout the data: check out the plot of the gaps 
>versus the mean value of the two endpoints and the same data mirrored in 
>1023/2 which I added to http://130.161.167.171/ethernut.zip
>
>Anyone?


I have looked at your data and it is a bit mystifying.  In the one graph, I 
believe I am looking at a time graph of data values as you sweep the 
pot.  The first 40,000 readings look like they are with the pot 
undisturbed.  Since you seem to get so much of a jump which would be due to 
noise, you could investigate that further without the complication of the 
wiper.  I see three (maybe four) discrete levels in this range.

Looking back at one of your original posts, it appears to me that your data 
bus may be scrambled.  If the data bus is serial, then I suggest that you 
look for a problem with timing in the data vs. clk.  If you are clocking on 
the wrong edge, you may see some problems like this.  I was almost 
convinced that it was a mix up of the bits on the bus until I looked at the 
raw data and realized that the four lowest readings were 0, 1, 3, 7 and 
15.  Yes, I know that was five values, I can't count.

I can't explain that sequence by a data bus scramble, but I can explain it 
by a problem with timing on a serial bus or possibly a problem with the 
voltage levels, pull up value or some other issue that would result in a 1 
bit smearing into other bit time windows.