1771 floppy controller questions

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Nov 20 02:41:17 2001

The model 3 has a 1793, which is very similar, but not identical. The 1771 has
an inverting data bus, and the MFM-capable version with an inverting bus is the
1791. I do believe I saw a message that indicated that BG Micro has the WD1771
for $4.95. I doubt there's a version that wouldn't work in the Model 1.

You're right, in that the model 1 expansion box is not a really common item.
I've not seen one in quite a while. They've probably gone to the great beyond
by now. The 1771 was quite popular, and had several second-sources, so perhaps
the NS part is worth a try. In the Model 1's single-density application, almost
any 1771 should work fine, though working fine doesn't really mean working
reliably. What I'd suggest is that you synchronize the data from the drive with
the 1771 by interposing a pair of 74HCT74's between the FD data in (after the
schmidt trigger) and the 1771, clocked with the fastest harmonic of the FD clock
that you can find on board. That forms a dual-rank register and synchronizes
the data in a way that has a good chance of improving the system performance.
You might confer with Tony Duell, as he's apparently persuaded the M1 FDC to
work fairly well. An upgraded data separator was quite a popular enhancement.

Dick
----- Original Message -----
From: "Tothwolf" <tothwolf_at_concentric.net>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, November 19, 2001 11:39 PM
Subject: Re: 1771 floppy controller questions


> On Mon, 19 Nov 2001, Richard Erlacher wrote:
> > From: "Tothwolf" <tothwolf_at_concentric.net>
> >
> > > I have a complete TRS-80 Model I that has a dead Western Digital FD1771-01
> > > chip in its expansion interface. Does anyone know if a National 1771-B01
> > > is a suitable replacement? What would be a fair/reasonable price for a new
> > > 1771 these days?
> >
> > You can get one for cheap if you go down to the thrift store and buy an old
> > TRS-80. That will cost less than a new WD1771, I'd bet.
>
> That conflicts with my ideals and goals on collecting/repairing these
> machines. The expansion interface for the model I also seems to be
> somewhat hard to find, as I haven't seen one in a thrift store in quite
> some time. The model 3 and 4 have a different 1771, which I seem to
> remember is not an exact replacement.
>
> This particular TRS-80 was given to me by its original owner some years
> back before he passed away. We had made plans for me to to pick up even
> more old stuff to go with it, but he died before that happened.
>
> -Toth
>
>
Received on Tue Nov 20 2001 - 02:41:17 GMT