RS232 (was: QL-Quality (Was: ZX-81 Question))

From: Hans Franke <>
Date: Wed Mar 27 08:12:03 2002

> > > > Well, Sinclair sold it and called it QL.
> > > > A 68008, running at 8 (?) MHz, (almost) Real Keyboard (at least as
> > > > good as most PC keyboards in the $10 range), Reak Memory (128K, as
> > > That does not make it a 'real keyboard'. In fact the QL keyboard I used
> > > was pretty unpleasant. My QL was obtained surplus as the bottom half only
> > > (no keyboard), so I kludged on a matrix of switches from my junk box.
> > > It's one of the few QLs with useable keys IMHO...
> > maybe, still you could work quite well.

> Well, I found the QL keyboard to be very unpleasant to use...

Well, let's agree on that it was not anything we would have payed
a lot of money for :=)

> > > You forgot to mention that the tape drives were very unreliable if used
> > > continuousely (those endless loop tapes would stretch and/or jam).
> > Right, but you could manufacture your own - using regular music
> > cassette tape of acceptrable quality did work quite well.

> Err, a serious business computer (which is what the QL was sold as in the
> UK, at least initially) does not require you to make your own media.

Over here it was ment as high class home computer, promising
to be even usefull for real applications.

> In any case, unreliability was still a problem. And I, for one, am not
> going to use a computer where I can't be certain of being able to read my
> files back again.

I wasn't the big QL geek, but as far as I used the machine, the
drives where reliable enough.

> > > The
> > > serial ports were broken as designed (I've looked at the schematics. The
> > > RxD lines from the 2 ports are just ORed together -- the external devices
> > > _must_ observe the handshake lines!), and
> > Which every _real_ device should do. That's what the handshake
> > lines are for. Always going for the least common ground isn't

Tony, as much as I apreciate your knowledge, now you
shoot yourself in the foot.

> Absolutely WRONG! Have you read the RS232 standard?

Yes I did, and I couldn't find any Note that they are just
funky add ons to till the sepc document.

> The handshake lines are _not_ there for flow control. After all, the
> RS232 interface was designed to link a terminal to a (dumb) modem. The 2
> devices that need to perform flow control are the terminal and the
> computer connected to the other modem. But the handshake lines are _not_
> transmitted down the phone line and thus can't be used (officially) for
> flow control.

Now you are talking about an end to end transmission, which
has NOTHING to do with RS232. RS232 defines the layout of
a serial line connection, and the behaviour of controll lines.

The interface is only defined for the connection between two
devices. And only between them. Whatever one of these devices,
like a modem, does with the data or not, is not part of it.
Of course the interface is especialy suited for communication
devices (modem) and got additional support therefor. Nonetheless
it's only about the communication between two pices of equippment.

The controllines are ment to tell the other sinde about states
like data can be accepted or not etc. Let's just take said modem
and terminal - flowcontroll here is to be made by using the hand
shake lines. As for example if the modem can't send the data fast
enough it needs a way to tell that the terminal has to wait.

> Of course everyvbody uses them for that, at least on local connections.
> But no device should _require_ them. It's one thing to allow them to be
> used to prevent data loss if too much data is sent too fast. It's quite
> another to require them to be used in all circumstances to prevent data
> ending up in the wrong place.

This sounds to me like asking car manufacturers to build their
wheels according to the request that the car should still work
fine if not all nuts are tightened.

> An example. Suppose you have a 30cps printer with a 9600baud serial
> interface. It's reasonable to use one of the handshake lines to indicate
> the buffer is full and that the host should stop sending data. But
> equally, it should be possible to ignore the handshake line and only send
> 10 characters per second (slowed down by software on the host, ignoring
> all handshake lines, just leaving large gaps between characters), without
> data loss. The handshake lines may (incorrectly) be used for flow
> control, they should not be _required_ in all circumstances.

Flow controll in the sense of RS232 is only about the communication
between the two connected devices.

> > the way to do.
> > > that the network was similar to the kludge used on the Spectrum.
> > Jep, but it worked. it is always easy to say XYZ is crap, not
> > as good as something else at 100 times the price. Remember, in

> Well, I would rather pay a little more money and get something that's
> useable. Spending money on something that doesn't do what I want is
> called 'wasting money'.

Agreed - just the QL did what expected.

> > > The QL was, alas, as typical Sinclair design. Built to a price, and it
> > > shows. It may have been reasonable to do that for a home computer where
> > > people couldn't/wouldn't afford anything better, but not for something
> > > that claimed to be a business computer.
> > At this scale, a Mac of the same time would also not qualify as
> > a business system ... not even cursor keys nor a numpad nor any
> > kind of interfase ... etc. pp.

> Hmm.. I regard the lack of reliable mass storage and useable serial ports
> (and no other I/O at all) to be rather more serious than the lack of a
> number pad (which, IIRC, was available as an option for the Mac).

Still, no real Disk drive (only the real weired Mac Drive,
not compatible to anything else, no hard disk (at a price
where one could get a CP/M System with HD), no accessable
system buss, no nothing. Only one serial port, and that's
it. Na, I didn't like the Mac (from a hardware point) back
then, an it didn't change over the years - the original Macs
are cloesed black box crap.

> > > > with Word Processing, Spreadsheet, Database and Business Graphics.
> > > > And all together at about 900 Mark (back than ~250 GBP). Lower
> > > It sold for \pounds 399 in the UK.
> > At the beginning ? I'm just asking, because I don't remember the
> I think so.

Well, at 400 GBP the QL was quite overpriced.


VCF Europa 3.0 am 27./28. April 2002 in Muenchen
Received on Wed Mar 27 2002 - 08:12:03 GMT

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