1 Sep
2005
1 Sep
'05
2:36 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org]On Behalf Of Dwight K. Elvey
Sent: dinsdag 30 augustus 2005 19:47
To: cctalk at classiccmp.org
Subject: RE: searching for replacement for 1793 FDC
totally none
Thanks for pointing that out Dwight! I overlooked that!
Only the 2791/93 has an *internal* clock divider circuit needed when
you control either 5.25" or 8" drives.
For the 2795/97 this means additional external circuitry.
I have in my design an octal latch to control some things, so density
can be controlled with one bit from the latch.
All in all, I will make my design with the (available) 1793. I only
have *one* trimpot adjustment, the 279x has *two*.
I will take the +12 from the power supply. The 7660 is a good suggestion,
but increases the chip count by one, unnecessary.
Ok, one wire added instead :-)
BTW, my design should work with 8", 5.25", and 3" proven years ago, so I
expect that 3.5" will work too ... time to heat up the soldering iron!
thanks,
- Henk, PA8PDP.
From: "Gooijen, Henk" <GOOI at
oce.nl>
> 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 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 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 ...
thanks,
- Henk, PA8PDP.
Hi
The 2791/93 are a more flexable choice than the 2795/97.
From my understanding of the spec sheet, the
2791/93 can
do both 5.25 and 8 inch without changing external parts.
The 2795/97 requires different clock frequencies to do
this.
You give up the side select but as was mentioned before,
I suspect that one could double up the direction bit
to also do side select or just have a port to do that.
Dwight