searching for replacement for 1793 FDC

[Gooijen, Henk]

> >>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
> >>    
> >>
> >
> >Thanks for the reply Holger.
> >Your remark about the +12 for the FDC // +25 for an EPROM programmer
> >is correct. I know of the existence of the 2797, but have totally
> >none experience with it what-so-ever.  The link that you gave is nice
> >but I am not sure I can *copy* the design ... Further, I have 
> >several 1793
> >  
> >
> Hi Henk,
> 
> What appears to make the design on that page a bit difficult is the 
> presence of the CPLD, but this is not really required, unless you
> need full SS30 compatibility, and at the price of losing some
> flexibility in setting modes; the 2797 datasheet shows a really simple
> application circuit.
> 
> >here, so that is cheap for me. I would need to buy the 2797 and ship
> >it to The Netherlands (sources here are not as good as in the US).
> >  
> >
> The 2797 is available from www.bgmicro.com, and they have no problems
> to sell to Europe; I have ordered several times from them already, and
> I guess if it works for Germany, it will also work for the Netherlands
> surely it is not useful for a single 2793, but they might have more
> attractive gadgets for the electronics enthusiast to reach a minimum
> order limit (had never problems WRT).
> 
> >The data separator I use with the 1793 is more stable, and built with
> >a VCO (LS629, LS393 and LS153).  I will look into the 2797 a bit more,
> >but I guess I'll go with the 1793.   I saw in the diagram of the 2797
> >that it has also 2 trimpots for the adjustment ... Not sure yet ...
> >  
> >
> They are for precompensation, and the datasheet explains how 
> to set them 
> - one better has an oscilloscope for it, but
> I guess this won't be better for a 1793 either.
> 
> Regards
> Holger


Yes, in my case you are better of with an 'scope too :-)
But I will try to find a way to get the adjustment OK without a scope.
Hmmm, that is -not- a promise ...!
(I got three 1793's from BG Micro yesterday in the mail)

  greetz,
- Henk.