searching for replacement for 1793 FDC

Holger Veit holger.veit at
Tue Aug 30 02:51:39 CDT 2005

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 (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.


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