Re: Apple ][ using PC floppy

[mdj <mdj.mdj@gmail.com>]

On Dec 31, 9:12 am, vladitx <vlad...@nucleusys.com> wrote:
> On Dec 30, 7:17 am, mdj <mdj....@gmail.com> wrote:
>
> > If driving TTL inputs is all you need, you can just put the relevant I/
> > O pins in open-drain mode and pull them up to 5v via a small resistor.
>
> The I/O pad still has to be 5V tolerant, irrespective of output being
> open-drain or something else.

The Spartan 3's have a Vin(max) of 4.4V, but the internal 3.3V pullup
will provide sufficient voltage for a 5v logic high.

As far as the other direction goes, a 10k resistor to limit the
current is all you really need, but if you're paranoid and/or have an
input device that'll generate a large Vh, a simple clamping diode does
the trick without having to resort to another SMD.

Matt