searching for replacement for 1793 FDC

[Scott Stevens]

On Tue, 30 Aug 2005 09:51:39 +0200
Holger Veit <holger.veit at ais.fraunhofer.de> wrote:

> Gooijen, Henk wrote:
> 
> >Hi all,
> >I am looking into the possibility to add a floppy disk interface
> >to the 6809 Core Board. 20 years ago, so this is OT :-) , I built
> >a floppy disk interface for my 6800 system using the 1793.
> >I have ordered some 1793 from BG Micro, but checking the data
> >sheet of the 1793, I noticed taht the FDC requires +12 on pin #40.
> >I know the MB8877 is pin-compatible with the 1793, but does *not*
> >need the +12V.
> >I failed to locate a seller for the 8877, but I do not know "all"
> >major part sellers in the US.  JameCo, BG Micro and DigiKey do not
> >have this part ... somebody knows a good stock of the 8877 ?
> >I can use the 1793, +12V is "ugly", but the voltage is present as
> >the +12V is needed for the floppy drive itself!
> >
> >  thanks,
> >- Henk, PA8PDP.
> >  
> >
> Has it really be the 1793? Or might not be a 2797 design (2797 is also
> 
> available from BG micro) from
> www.swtpc.com/mholley (New design for SS30 FDC) is more appropriate
> for "new developments",
> given that it doesn't need that really ugly external data separator 
> logic which always prevented me from
> building FDC boards (a usable separator chip is more difficult to find
> 
> than the FDC chip, and the alternatives
> with a TTL-monoflop grave is not even more attractive).
> 
> Actually, what is your real problem? You already have 12V for the
> floppy drive, so what prevents you from
> feeding it into pin #40 of the 1793? +12V on an otherwise +5V board is
> 
> not more ugly than a +25V source
> on an eprommer board, or +12/-5V for 2708/4116 memory boards.
> 
> Holger
> 
And even if there's no 12 volts on the logic board itself, it's pretty
easy to install one of those 'charge pump' type chips (I think Dallas
Semiconductor is one source) that uses outboard capacitors to boost your
5v supply and give you the needed 12 volts.

I just did a quick search using 'ICL7660' as the key and yes, Maxim
still makes this beastie, which would serve your needs.  

Datasheet at:
 http://www.ee.washington.edu/stores/DataSheets/linear/icl7660.pdf

Maxim's web page for it:

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1017

Gawd, why do I have part numbers like '7660' taking up valuable wetware
space??