In general, Western numbered their FDC's such, that their parts had odd
numbers on the "normal" parts. The mainstream FM-only part was the 1771,
which is what was in the RS Model 1 and which used +12 on one of its 40
pins. It had an inverted data bus.
The 179x series was more fully developed, in that the 1791 was a 40-pin part
using +12 but which was MFM-and-FM-capable, but required external data
processing to apply precomp on writes and to extract clock from the raw data
stream on reads. Like the 1771, it had an inverting data bus.
Western also made a 179x member or two that had non-inverting data ports.
These were the 1793 and 1797. These were like the 1791, and 1795, which had
the inverting data port, but of which the 1795/97 was intended for use with
two-sided drives. The 1793 and '97 had noninverted busses, while the 1791
and 1795 had inverted busses, and the '97 and '95 had a head-select
provision not provided internally in the other (lower) numbers.
The 1770,1772, and 1773 are/were 28-pin parts, using 5-volts only, and
equipped with heavy duty drivers capable of driving the FDD cable, while the
40-pin parts required external buffering. The 1770/72/73 had internal
data/clock separators and write precompensation logic. They were clearly
intended for use only with 5-1/4" drives, as they had provision for the
motor-on signal, with the exception of the 1773, which differs slightly.
There was also a 1774 that I read about at one time, intended for use with
M^2FM which didn't make it to market. I've never seen one, however.
Dick
----- Original Message -----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, May 30, 2000 5:10 PM
Subject: Re: Defining Disk Image Dump Standard
> >
> > Rumor has it that Richard Erlacher may have mentioned these words:
> >
> > >Just as an aside, I recently encountered a datasheet for the WD 1773
FDC
> > >(similar to 1770/72). Do you know of any systems in which it was used?
> >
> > Wasn't the 1773 a single-chip version of the 1793, or am I out in Left
>
> Basically, yes. I know I have the data sheets in my Western Digital
> Databook (along with the 1770, 1771, 1772, 179x, 279x, and some hard
> disk controller chipsets). But I'm not going to go and find said book
> unless you need things like pinouts, etc.
>
> > Field? The early Tandy controllers that required 12V were based on the
> > 1793, and weren't the later 5Vonly ones based on the 1773?
>
> For the CoCo, yes. The older one had a 1793, and needed 12V (which means
> it didn't work on a CoCo 2 or 3 without a hardware mod to the computer,
> or the use of a multipak interface). The later ones used the 1773 and
> only needed +5V.
>
> But other TRS-80s used other controllers :
>
> Model 1 : 1771 (together with a 1791 if you had a double density mod)
> Model 2 : 1791 (I think -- it was a 179x series)
> Model 3/4 : 1793
>
> -tony
>
Received on Tue May 30 2000 - 19:15:22 BST