Lpc2000

You can also use a pull up resistor to 5 volt, and switch the gpio 
between low output and input. This works because the GPIOs are 5 volt 
tolerant (don't do this with an adc capable pin, see the errata for 
explanation).

Richard Duits.


javida13 wrote:

> Yes, I did mean VIH.  I forgot to preview before I posted.  I'm
> interfacing to a Futaba LCD Emulator.  Some of the inputs are spec'ed
> at 0.8*Vcc and others are at 0.7*Vcc Min.  I checked with an App
> Eng at Futaba USA and he indicated that 3.3 volt logic will not drive
> the device. Since I only have 3-signals to this device (serial
> interface), its probably safe to use a AHCT125 device.  The only
> problem is that the data I/O line is bi-directional therefore an
> additional GPIO is required for this input.
>
>    Barry
>
> Peter Jakacki <peterjak@t...> wrote:
> > Vol ??? You do mean Vih, don't you? In my experience I've never had
> a
> > problem with driving 5V logic from 3.3V as the minimum Vih in is
> > specified for full-speed digital switching. The 3.3V definitely
> drives
> > the 5V logic as a logic high but it may not work to "parametric"
> > specification at 100Mhz etc. For all your normal I/O work it is
> never a
> > problem and I don't let myself lose sleep over it.
> >
> > You can though for peace of mind and sleep use pull-up resistors to
> +5V
> > on the output lines and simply simulate open-drain drivers by
> writing
> > the IODIR. It doesn't matter if you initially drive them to 3.3V
> and
> > then float by switching to inputs with the pull-up. IMO, skip the
> > buffers, they are always overkill.
> >
> > my2cents
> > *Peter*
> >
> > p.s. Hey Rob! I dug out the TI yellow bible and mine is dated 1988.
> I
> > also remember my first logic data book, it was a big red Fairchild
> > Semiconductor TTL data book from the early '70s. Back then you
> needed
> > PSUs that could supply amps, none of this itsy-bitsy pencell
> battery
> > stuff! Plus you had to worry about fanout (both the blower type and
> > driving type).
> >
> >
> > javida13 wrote:
> >
> > >I have a 5 volt logical display that I'm driving.  The Vol for
> this
> > >part is 3.5 volts (.7*Vcc).  I have 3-signals that must be driven
> to
> > >this logic level.  Is there a LS type of device that can be used as
> the
> > >level translator, where is can be powered by 5 volts and its input
> > >level can be driven by 3.3 volt logic?
> > >
>
>
>
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