Lpc2000

--- In lpc2000@yahoogroups.com, "dijucthat" <bigdaddy81@...> wrote:
>
> I have a project that was setup for a 5v AVR that I would like to 
> convert to an LPC2294.
>   
> Q1: Is it better to use a simple voltage divider on the GPIO Input 
>(to  get 3.3v) or should I leave it at 5v? (I know it says 
> 5v "tolerant", but is it safer at 3.3v)
> Q2: On GPIO outputs, can I use a pullup to get 5v, or should I use 
> a buffer, ULN2003, etc.? (again, I am concerned with reliability)



Umm... may be..
On LPC, to output a '1' with 5V pull up:
- Set output bit to 1 (this will drive output to 3.3V)
- The output will not go >3.3V as Upper PMOS transister seems to
  be sinking current from external 5V pull up when on.
- Once the Output is forced to 3.3V by an active pullup transistor,
  set the port bit to input.
- The external pull up resistor will then pull to 5V, slower.
  (Do not let port pin be output, it will not get pullup up to 5v)
- Hope this will be "quite" similar with your AVR port pin with 
  both active (for few clocks) and passive pullup
- ...Actually, I've not tried this on LPC yet...
To output a '0':
- Just set port bit to '0' and configure port pin to output.

(Hope philips will use I/O direction to control I2C ports instead
of open drain outputs.  Then we could have push-pull outputs on
all I2C pins)



> Q3: On the sensors designed for 5v operation, is an op-amp with  
> gain <1 the best solution to achieve 0-3.3 scale?



Pls use opamp configured for lo-Z output and drive the ADC inputs.  
We (including me) have lots of ADC input impedance problems but
not yet confirmed by philips.   The AVR parts has extremely hi-Z
inputs for the ADC.


> Q4: On the ADC inputs, I have read that you should ues pullups
> even if they are not in use.... does this apply to all LPC? 



Could you just configure those pins to output and set port bit
to '1' or '0'??

Hope it helps!   
Pls let me know if you have better ideas  :)
Regards


> 
> Thank you very much for any response!
>   Daniel.
>