[ts-7000] MAX197 Sampling Rate/Inaccuracies

["garaloha211" <>]

I have been testing the functionality of the TS_7250 and have run 
into issues while sampling analog inputs with the MAX197.

I have been able to collect a single sample accurately. However, 
when I put the same code into a loop, the first sample is accurate 
and the remaining samples are some constant #.  (see code and 
execution results below)

for(n = 0; n < num; n++)
{
   *control = hexVal;    //control value
   // Wait for the conversion to complete
   while((*complete & 0x80) != 0)
   // now store the result on a scale from 0-(2^12-1) in sig array
    res = 0;
    res = *lsb;
    res |= *msb << 8;
    sig[n] = res;
}

When executed on chn 0 with range from 0-5v and a constant 1V input 
the results of 20 samples were as seen below.
result: 848
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832
result: 832

I have consistently had this result with several different inputs 
(AC and DC all within correct range).  I have tried adding a sleep
(1); at the bottom of the loop and found that slowing down the loop 
execution yields accurate results but not reliably and I need a much 
higher sampling rate than 1Hz.

Can anyone provide me with some information on this problem and 
propose a solution?

Also, I have seen in the TS-7250 manual that the control register 
for the MAX197 is at 0x1080_0000 (page 29 JUN 2007).

However, in the example code (page 39 Linux for ARM JUL 2007), 
0x10C0_0000 is used to map the control.

I have tried both and seen that each value 0x1080 and 0x10C0 works, 
at least for the single sample case.

Which address should I be using to properly control the MAX197 chip?

It is critical that I am able to maximize the sampling rate of the 
ADC.  Please advice on the best solution.

-Thank You




 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/ts-7000/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/ts-7000/join
    (Yahoo! ID required)

<*> To change settings via email:
     
    

<*> To unsubscribe from this group, send an email to:
    

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/