1 Sep
2005
1 Sep
'05
2:55 a.m.
>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
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