Lpc2000

Em Qua 15 Mar 2006 15:06, dijucthat escreveu:
> 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)

I made some tests with 5V, including 5V RS232 signals (from MAX232) including 
ISP and I had no problems until here.

> 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)

A pull will not work. If you put it, on the pin you will have 3V3, even 
configuring the pin to output (high) or input. I dont know for sure, but all 
the ICs I know have a diode from the pin to the IO supply. So, to have 5V as 
output, you will need a buffer. 

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

No. If you use a rail-to-rail opamp, with the input at 5V you will have maybe 
4,9V on the output, in the best case. The same for a signal at 0V. If you 
can, put a resistor divider. That means a lot of problem, the principal are 
current leackage over the resistors, the current leackage from the AD input, 
and the imprecision of the resistors over the temperature. If you need and 
opamp, the best is to use positive and negative supplys, and greater than the 
signal you will apply.

> 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?

If you have a pin that will remain as input, ALLWAYS put it on a known state, 
never leave him open. A pullup is a good choice, I am working with LPC2106 
which does not have AD, and I didnt read the 2294 datasheet, but maybe you 
can put him to ground. 

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

I hope I helped (I am a newbie too!)