Re: Apple ][ using PC floppy

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

On Jan 1, 3:11 am, vladitx <vlad...@nucleusys.com> wrote:
> On Dec 31, 8:18 am, mdj <mdj....@gmail.com> wrote:
>
> > 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.
>
> 4.4V is absolute maximum, point beyond which you're damaging the gate
> oxide.
>
> Look at "Iik" parameter - Input clamp current per I/O pin. It's rated
> at max 100 mA for input range of -0.5V .. Vcco + 0.5V.
> WIth Vcco = 3.3V the clamp current is rated only up to 3.8V. Consider
> also few pins' clamping diodes conducting simultaneously.
>
> I think you either need external buffer or count on the 3.3V be enough
> to feed TTL input (all trace length/load considered).

As an open drain, it's ample for TTL; I wouldn't count on it for
source inputs however (never tried it)

> > 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.
>
> The internal ESD clamp or external one?
> There are also big spikes generated by RF noise (cellphones, etc).

External. I have use a large box of signal diodes, resisitors, led's
when doing stuff like this in concert with a couple of IDC->DIP
adapter cables so I can easily breadboard prototypes.

Matt