2 Apr
2001
2 Apr
'01
11:15 a.m.
Actually, the ST412 physical interface is, unless I've missed something in the
(insert ridiculously large number here) times I've done it in every way
identical to the ST506. The only difference I've noted is that the
ST412-series drives were capable of buffering the step pulses in order to
compute fast seek velocity profiles. This is a firmware effect, not a hardware
one, though the hardware had to be somewhat different. The controller local to
the drive could, therefore implement some sort of PID algorithm.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Monday, April 02, 2001 3:25 PM
Subject: Re: D connector tirade (was: Re: Age-old ethernet equipment)
of
lots
The PC-generation wasn't when this started. I'm about (once I have time)
to sit
down with my S-100 hardware and produce logic analyzer snapshots and import them
into my PC so I can use them in documenting what REALLY happens on the bus with
each of a number of CPU boards. My experience has been that the documentation
provided with CP/M-era hardware was often fraught with error and even with
disinformation. The situation with PC-generation stuff seems to have been that
the mfg's simply saved themselves the trouble of publishing disinformation about
their products, since the PC was designed for people who'd see a logic diagram
as being a foreign language anyway.
>
> You're certainly correct in that publishing a bit of information in a
particular
> place doesn't make it fact. However, calling
the small serial port
connector
commonly seen
on some DEC and all PC/AT equipment a DB9 is definitely wrong.
Agreed. No way is that connector a DB anything....
As for incorrect information in print, PC-related books seem to be about
the worst for this. I've lost count of the number of such books that
contain misleading and just plain wrong information (much of it a lot
more serious than the DB/DE confusion). Another 'favourite of mine --
NOT' is the 'MFM hard disk'. As I understand it, MFM refers to a
particular encoding scheme used to write bits on the disk and has nothing
to do with the interface. It is perfectly correct to talk about a SCSI
MFM drive, meaning a drive with a SCSI interface that happens to use MFM
encoding to write data to the disk.
But the PC crowd seem to use (have used?) the term to mean a drive that
is designed to use MFM encoding at a 'raw' interface that is similar to
the de-facto standard defined by the ST412 hard disk. And which is
somewhat less similar to the interface on the ST506 hard disk (which is,
of course, the other name that it is often called). I remember <mumble>
years ago buying a disk drive for my PC/XT and having a lot of difficulty
explaining just what I wanted.
> The notion of naming sub-d connectors for the shape, shell size, and number
> pins certainly went down the toilet when they
started packaging the same
shell
with pins of
differring position density. This notion was started by one
There's no problem if you use the number to mean the total number of
available pin positions. Rememebr that the crimp-pin connectors, where it
is common to only populate some locations, came out a long time after the
original D connectors, which had all the pins (solder connection type)
fitted at the factory. So originally the number of pins and the number of
possible pin locations were the same. It's not clear, therefore, which
the number refers to.
If you use that convention, then there is no problem. A DE9 is a PC/AT
serial port, a DE15 is a VGA monitor port and a DA15 is a joystick port
(if you'll forgive me being PC-centric for the moment).
> > [2] I am not sure how anyone can write a hardware book without a single
> > schematic or timing diagram, but the PC-crowd seem to manage it.
> >
> They have to write what their intended readers can understand. After all,
OK, but if I'd not call such a book a 'hardware bible' or a 'hardware
reference'. Those terms should imply some technical information...
The people willing to buy and rely on such things get what they deserve. Most
of them don't read the things anyway.
And don't get me started on so-called service manuals without schematics,
or timing diagrams, or even complete and accurate block diagrams. The
Torch XXX manual is probably the worst -- it doesn't contain one piece
of information that is not obvious from looking at the machine, and it
seems to bave been written for somebody with a mental age of 2 (and
that's being kind).
A catchy title will sell products so abysmally lacking in both value and
underlying knowledge that anybody who would actually read such a thing would be
appalled.
Apart from the IBM Technical Reference manuals (which are excellent,
although rather dated), is there a good book on PC hardware? Because I've
yet to see anything I would spend any money on...
Frankly, I've yet to see a good book on PC-anything.
> of people have made lifelong carreers of hooking up computer equipment
without
> ever concerning themselves with a schematic or
logic diagram. Conflicting
> practices made this difficult, but by staying with a single vendor, one
could
eventually
figure out what each connector at the bulkhead represented, e.g.
DB25S meant DTE, DB25P meant DCE, and so on, and do pretty well with that.
It's odd, but I've never had any success doing things like that, even
when I use so-called compatible parts. But if I get the pinouts, and sit
down with a logic analyser (if the timing diagrams are not available), I
can generally get things to talk to each other.
-tony