If you wanted to preserve the sense of the data bus, you'd use a 1791, which
also has the inverted data bus. The 1791 and 1793 are otherwise identical.
It's pretty straightforward upgrading a 1771 with a 1791, with the exception
of the write precomp and clock/data separation logic, which has to be
upgraded. I find the SMC9229 a fine solution. It also muxes the clock to
the appropriate harmonic of the 179x clock.
Dick
----- Original Message -----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, May 30, 2000 6:12 PM
Subject: Re: Defining Disk Image Dump Standard
> >
> > The 'Shack model 1's had a 1771 and the model 3's had a 1793. These
were
> > nearly pin-compatible, both on a 40-pin footprint and required buffering
to
>
> One big pin-compatibility difference is that the 1771 had active-low data
> pins, and the 1793 had active-high data pins. The 1791, with active-low
> data pins, was closer to the 1771, therefore, and was what was used in
> the Tandy double density mod.
>
> -tony
>
Received on Tue May 30 2000 - 19:39:31 BST