Lpc2000

You did not say which part you are using. The issues with the ADC pins 
not being fully 5 volt tolerant may be solved in the newer parts 
(LPC214x, etc).

The others items were things I would check or do diffirently, I had no 
idea if they are the cause of your problem. Are you sure the conversion 
starts? You can add a counter to the wait loop to see if it waits a few 
cycles. If it doesn't, you did not start the AD conversion and you need 
to check the value you write to the ADCR register.

Richard.


Sutton Mehaffey wrote:
> Richard,
>
> I had these set up in an init file that I didn't include with the code.
>
> Also, it didn't matter if I did the write to AD0CR all at once or
> separate.  No change in the data.
>
> I couldn't find anything in the errata sheet.  I printed out Errata
> 1.2 released on 2/27.  Where is the errata you were referring to?
>
> Sutton
>
>
> IODIR0 &= 0x8FFFFFFF;   // AD0 (P0.28, P0.29, P0.30) defined as inputs
> PCONP |= 0x00001000;    // Enable AD0
> PINSEL1 |= 0x15000000;  // AD0.1, AD0.2, AD0.3 all defined
>
> AD0CR = 0x01200404;
>
> // AD0CR |= 0x00200000;  // turn on AD0
> // AD0CR |= 0x00000400;  // divide 12Mhz clock by 3 (max 4.5Mhz ADC clk)
> // AD0CR |= 0x00000004;  // select channel AD0.2
> // AD0CR |= 0x01000000;  // start conversion now
>
> while ((AD0STAT & 0x00000004) == 0);  // DONE2 status bit in AD0STAT
> result = (AD0DR2 & 0x0000FFC0) >> 6;  // bits 6-15 are result (0-2055)
>
>
>
>
> --- In lpc2000@yahoogroups.com, Richard Duits <yahoo@...> wrote:
> >
> > You should start the AD conversion with a single write and not a series
> > of read-modify-write operations.
> >
> > Also make sure that none of the ADC capable pins stay below 3.3 Volt
> > even if they are not used as ADC inputs (see errata for more info).
> >
> > Make sure you configure the pin as ADC input with the pin configuration
> > registers.
> >
> > Regards,
> > Richard.
> >
> >
> >
> >
> > Sutton Mehaffey wrote:
> > > Please help us to improve Yahoo! Groups. Take the survey now!
> > > <http://v2.decipherinc.com/survey/yahoo/yah05014?list=18>
> > > I am trying to read a battery voltage (~12V) on AD0 channel 2.  I have
> > > a breadboard circuit with a voltage divider that is working properly
> > > that gives a reading between 1.8V and 2.3V more or less.  I am using a
> > > variable power supply to generate these voltages.
> > >
> > > When I connect the 1.8-2.3V to P0.29 (AD0.2), I read CFF (all 10 bits
> > > high) no matter what.  Can someone tell by the code below if I have a
> > > setting wrong?  My PCLK is 12Mhz.
> > >
> > >
> > > AD0CR |= 0x00200000;  // turn on AD0
> > > AD0CR |= 0x00000400;  // divide 12Mhz clock by 3 (max 4.5Mhz ADC clk)
> > > AD0CR |= 0x00000004;  // select channel AD0.2
> > > AD0CR |= 0x01000000;  // start conversion now
> > >
> > > while ((AD0STAT & 0x00000004) == 0);   // DONE2 status bit in AD0STAT
> > > result = (AD0DR2 & 0x0000FFC0) >> 6;   // bits 6-15 are result
> (0-2055)
> > >
> > > DONE2 is set, and result is always CFF.
> > >
> > > Sutton - dodge1955
> >
>
>