[ts-7000] Confused about 7250 A/D

["naturalwatt" <>]

I am very confused about how the A/D works on the 7250.  Reading the Linux 
Developers 
Manual it talks about an a2d_driver.o, which is not present in the 
lib/modules/kernel 
hierarchy nor in the source tree for ts11.

There is a helpful example here, the adc_7250 program, which works as 
advertised, using 
direct memory access.

The description in the 7250 Manual, and the EP9301 User Guide, implies that you 
read in a 
32 bit value and must blank off all but the lower twelve bits. (0xFFF). 

The adc_7250 program masks off 16 bits, using 0xFFFF, and include logic like 
this:

                if(avg < 0x7000)
                        avg = avg + 0x10000;

                if(virgin == TRUE)  //use approximation
                {
                        avg = avg - 0x9E58;
                        val = ((double)avg * 3.3) / 0xC350;
                }

I am getting raw values like this:
0.2V   40921  0x9fed
1.6V  248     0xf8
3.3V  25122  0x6222

The above C code converts the raw values, but I don't understand why.  Surely 
the raw 
values should go from 0x000 to 0xfff, from 0V to fullscale?

What am I missing?

Thanks in advance,

Martin









 
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