? There are no Teletypes that use Baudot code. They use a US variant of
? the ITA2 five-level code.
? Baudot code was only used until about 1901. Murray code was used until
? the 1930s. Everything after that used ITA2.
That's a little like saying nobody actually uses ASCII since 1968, we're all really
Using ANSI_X3.4-1968 or later. Technically true but not common usage.
Everyone in the past half century has called a Model 28 TTY a Baudot Teletype when
They had to distinguish it from any other type. (Baudot is still the default for
Several applications so you don't even have to say it's Baudot.)
I suppose classiccmp naturally attracts folks who care about such things (witness
The thread I started over a few years ago when I noted that bitsavers had surpassed
100 GBytes and everyone informed me that no, a Gbyte was 1073741824 bytes so
I was wrong.)
Tim.
Hi guys,
Is there a defined standard as to when the READY output on a
Shugart-type disc drive should go active?
I'm (slowly!) working through the rebuild of one of the Amstrad drives
(an EME231 I know to have working mechanical components, potentially
good heads, and a fried control board), and I'm stuck on deciding how to
deal with the READY output.
My initial thought was to hold it inactive until a few INDEX pulses have
passed, and the motor speed was within 5% of 'ideal' speed. The plan was
to use a 32kHz oscillator and a 4040 counter to get a several-Hz signal,
then rig up some logic to check that the disc speed was OK, and after a
few valid index cycles enable the drive.
Then I started wondering... am I over-engineering this? Would waiting
for a couple of full disc rotations be enough to reliably generate a
READY signal?
Irony is that the read-amp will probably be the easiest part of the
whole system... I've got a Motorola appnote which basically says "if
you're using a data rate of X and a rotation speed of Y, these
parameters will work" -- X and Y being the two parameters the Amstrad
drive uses... That just leaves the write amp and erase logic to design
(and maybe a 'write lockout' jumper).
Thanks,
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
Eric wrote:
>>> There are no Teletypes that use Baudot code. They use a US variant of
>>> the ITA2 five-level code.
>>> Baudot code was only used until about 1901. Murray code was used until
>>> the 1930s. Everything after that used ITA2.
Tim wrote:
>> That's a little like saying nobody actually uses ASCII since 1968,
we're all really
>> Using ANSI_X3.4-1968 or later. Technically true but not common usage.
Eric wrote:
> No, it's not much like that at all. Baudot code used significantly
> different character encodings than ITA2, such that a Baudot device and
> an ITA2 device will not interoperate in any meaningful fashion.
> ASCII-63, ASCII-67, ASCII-68, and ANSI X3.4 have only minor variations
> and will generally interoperate reasonably well.
I'm not disagreeing that the academically correct term is ITA #2. (Interestingly
most web page hits today call it "ITA 2" or "ITA2" but the 70's and earlier
books call it "ITA #2" when they are being pedantic.)
I'm just saying that in its Heyday, if you had to distinguish a 5-level
TTY from a 7-level TTY, the working terms were Baudot and ASCII. Although
technically incorrect.
Sort of like when I know the people who used and maintained what they
called a 11/74, and then I see folks here telling me that no, it's really
A 11/70MP :-). Yeah, in a certain aspect that may be what the paperwork called
it. But really everybody called it the 11/74. When I'm told that the
academically correct word for something, is different than what everyone
actually called it at the time, and I see Wikipedia etc. going for academically
correct rather than "actual working term", it sometimes feels like history
that I lived is being redefined underneath me by some sort of pedantic streak.
Another recent example of a different character set being redefined underneath
Me: On Wikipedia, the morse code for -...- is defined as "double dash" with a
Possible keyboard equivalent of "equals sign", something I never heard
till recently. I called it "BT" with a bar
Over top for most of half a century now. I don't doubt that some CCITT standard
Called it double dash in the past, just that me and the guys I know who use
Morse every day, never called it that.
This isn't new to me. I remember getting involved in altmode vs escape key arguments
In the distant past. I always called it altmode, what right does anyone else
Have to call it escape? :-))))). Big smileys, because I discovered that three
Different ASCII codes (0174, 0175 and 033) were being used and I didn't know until
Much much later.
Tim.
>
>My initial thought was to hold it inactive until a few INDEX pulses have
>passed, and the motor speed was within 5% of 'ideal' speed. The plan was
>to use a 32kHz oscillator and a 4040 counter to get a several-Hz signal,
>then rig up some logic to check that the disc speed was OK, and after a
>few valid index cycles enable the drive.
>
The BBC Micro internally generates the ready signal for the 8271 controller
>from index, drive select and the 8MHz clock using a 74LS393, 4020 and 4013.
I figured out how the circuit works once and my head still hurts. As far as
I remember, it works like your description above and if an index pulse is
a few percent later than expected, it deasserts ready.
This was designed for 5.25in floppies and worked fine with early 3.5in
drives. However a problem arose with more recent 3.5in drives. It
seems that instead of requiring a particular time between step pulses,
these drives allow the controller to step as fast as it likes and they
signal the controller that the heads have not yet reached the required
location by suppressing index until they do. The circuitry in the BBC
notices the lack of index and drops the ready signal to the 8271 resulting
in a "drive not ready" error when stepping by more than a couple of tracks
(er, I mean cylinders) when using one of these drives.
It seems the lessons are firstly that the designers of the BBC micro did
not reckon they could rely on getting a good ready signal from the drive
and secondly, no matter how you try to be clever, something will later
come along to mess up your cunning plan.
Regards,
Peter Coghlan.
Actually, the Rayovac 840 is rated at 4.5v 800 mAh, so putting in
3*AAA is a reasonable (and "cost effective") thing to do. But the
footprint is a tad larger. There's room...
The NetBSD pages specifically mention a FCT623 as the cause of
problems but I didn't want to get into that mess unless I had to... A
Linux FAQ claimed that changing the video or serial cables could also
cause problems.
> The big minor thing is the back panel to the stand. It's missing
Bill, we have several *SR-33 "parts" machines; I'll mail you a back
panel for the stand. Send me your address in a private message.
Brent wrote:
> Some minor changes were made to the Murray encodings and it became the
> ITA #2, but referring to it as Baudot code continued for general
> reference. In other words (like so many other things), both terms would
> seem reasonable or 'correct' depending on the perspective one is coming
> from.
I will note that from an academic/historic standpoint that MacKenzie's _Coded Character Sets: History and Development_ calls it CCITT #2 and I don't think he uses the word Baudot at all.
But I also feel that MacKenzie's book is written almost entirely from a standards-committee mindset. There's occasional mention of "real world usage after the character set was standardized" but it's brief.
Tim.
> I remember my first computer experiences were in terminal rooms full of
> teletypes. You realised just how noisy they were when the machine (a
> DECSYSTEM-20) went down and all the terminals stopped at once. I would love
> to get hold of an ASR33 but they seem pretty rare these days.
Don't forget THE SMELL of a room of working model 33's. I'm not sure
exactly what the smell was - probably a mix of ozone from the motors,
warm oil on the mechanical parts, and some of the smell of oiled
paper tape - but that was part of the experience too :-)
Oiled paper tape could actually go rancid under some conditions
(that I'm unclear about today!). I wonder if that's one of the smells
I remember. In particular the smell from the hoppers that
Caught the holes punched from the tape as being not the typical
Teletype smell but something stronger and more offensive. The hoppers
Were not necessarily emptied daily :-)
Tim.
>
>> The datacenter was always at 62 degree's, after working 4-5 hours in
>> there, your knuckles started to stiffen up and you'd feel the cold from
>> the floor come up into your shins... ah.... good times, good times :-) I
>> loved the quietness, all you heard was the sounds of fans whirling away,
>> it was a deafening kind of quiet background noise, I miss that.
>
> It really is a good feeling. Only true geeks seem to appreciate it,
>though.
>
My last boss, who was from the sales end of the organisation occasionally
had to help me move stuff in our data centre. He didn't mind the heavy
lifting but he really hated being in the place. It didn't bother me at all,
especially if the office was hot and sticky.
What I miss is from 20 years ago, in a different place, the 400Hz drone of
power supplies in equipment connected to a motor-generator set. Never mind
the video - does anyone have a sound recording of that?
Regards,
Peter Coghlan.
