Lpc2000

Q2 is probably the only one I feel confident to comment on:
I would use a 74HCT logic gate to buffer the output if the
target swing is 0 to 5V. If there are a lot of lines to
buffer you can't go far wrong with a 74HCT373.
Unless, that is, you intend to drive relays or the like
when a ULN200x really shines.

For bidirectional lines (where I can have a pin that says
which direction I want) I use a 74LVC4245A and it seems to
work.
In the past I have tried (and failed) to use an ADG3308
"automatic direction-sensing" bidirectional level shifter.
I'm not suggesting that it can't be made to work, but do
breadboard that chip before getting a PCB made. I would
be grateful for comments as to what I might have been
doing wrong with the ADG3308 because it seems so useful!

I think the data sheet says GPIO pins are only 5V-tolerant
when the 3.3V supply is present. (Quite what will happen
when it is not present I'm not sure, but that's what I read).
Since my +3.3V is derived from the +5V I don't worry about
this.

As to unity0724's hope that (when used as GPIO) the I2C
lines can have pull-ups, the complication is that an I2C
device must not load the lines when its power is not present.
The easiest fix for this is to omit the pmos output
transistor altogether, and this is what Philips do.
Other approaches might be possible but I can't think how.

Regards,
Danish
--- In lpc2000@yahoogroups.com, "unity0724" <unity0724@...> wrote:
>
> --- 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.
> >   
> > 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)