Re: Microsoft Softcard with NEC Z80 clone?

["RedskullDC" <RDC@oz.org>]

"Sean McNamara" <sean@macassist.com.au> wrote in message
sean-033A23.21392406112004@news-server.bigpond.net.au">news:sean-033A23.21392406112004@news-server.bigpond.net.au...
> Hi folx,
>
> I've found a Microsoft Softcard with an NEC D780C-1 (see
> <http://www.cpu-world.com/CPUs/Z80/NEC-D780C-1.html>) which appears to
> be 4MHz - I'm assuming the card would be the usual speed of 2MHz - or
> would it benefit from the faster Z80?
>
> Was this a standard version of the Softcard, or has someone changed
> chips somewhere along the way?
>
> Thanks
>
> Sean

Hi Sean,

Nothing special about the NEC chip, that is just their part number
for their Z-80 compatible chip.

The Softcard (and compatible clones) require the 4MHz part because
the clock signal sent to the Z-80 on the card has a non-symetrical
duty-cycle. ie: it is not a regular square-wave.

Cheers,
Leslie