25 Sep
2011
25 Sep
'11
5:19 p.m.
On 25 September 2011 18:56, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Sure, other machines used that connector later. But surely it was called
the 'PS2 keyboard conenctior' becuase the first machine to use it was the
IBM PS/2. Had it been first used on an HP Vectra, say, I guess we'd call
them 'Vectra keyboards'.
Sure, yes, absolutely. I don't see why or how that contradicts me at all.
That is my point. They /are/ similar protocols, so that (eventually)
they were made interchangeable.
Serial-stroke-PS/2 mice never were. You couldn't use a Logitech
serial-to-PS/2 convertor on a Microsoft hybrid-port dual-protocol
mouse, for instance - I tried.
(Later, this worked too - some /de facto/ standard was worked out, I guess.)
Hang on a second. Logically, a 'PS/2 keybaord'
is one that works on a
PS/2 computer. A PS/2 mouse is simularly one that works on a PS/2
computer. There is no reason to assume that the interfaces must be simi=
lar.
Firstly, no, it was not just for PS/2s; fairly soon after the PS/2, other machines
took it, and a few years later, /all/ PCs used the same
connector.
Secondly, yes, the interfaces were close enough to the same that some
BIOSes would actually display an error message saying "mouse inserted
into keyboard port" or /vice versa/. Helpful but not as helpful as
just bloody working with it, whatever socket it was in, would have
been.
Actually, that doesn't imply the signals are simular, only that the
machine can detect what's plugged in to a given socekt.
At one time there were mice that could work on both the PS/2 standard and
on an RS32 serial port. Typically the mosue cable ended in a 6 pin
mini-DIN conenctor, there was an adapter packed with it that had a DE9
socket on one sida and a 6 pin mini-DIN on the other. And in most (if not
all) cases, thei swas a simple adapter linking pins on the 2 conencotrs,
it didn't contain any circuitry.
But the Rs232 interfce is not remotely close to the PS/2 mouse interface.
It even uses different voltages., The mouse was designed to work out what
it was pluggedf into (possibly by detecting said voltages) and outputted
data accordinging.
Now, as it happens, the PS/2 keyboard and PS/2 mouse protocols are almost
identical. The IBM PS/2 TechRef is not nearly as good as the ones for
older systems, but it does have some useful information. And it shows
that hte bit-level protocol is the same. The IBM keyboard/mouse interface
chip in the PS/2 could talk to both devices, there were commands to
enaable nad disable them, etc. And it identified which device had sent
the data when you read the incoming data from it. AFAIK it is the other way round. When I was fixing an
Olivetti Sparkjet
printer, I needed a dual infrared sensor, and the easiest way to get one
quickly was to buy a cheap optomechancial mouse and strip it. The mouse I
bought was aPS/2 one (that was the chaepest one I could find in Maplin),
the cable.plug is still in my junk box and the plug is green.
You are quite right.
As I said abouve, that's a non-sequitur. All you
can conclude is that the
machine can work out what it's conencted to and handle it accordinhly. It
doesn't imply antthing about the interfces being the same. In fact they
are very similar, though.
That's the point.
I'm not saying that the PS/2 keyboard interface (hardware *plus*
protocol) was /the same as/ the PS/2 mouse interface, but eventually,
they /were/ made interchangeable. But the two slightly different
interfaces - K/B S/W+H/W combination and the mouse S/W+H/W combination
- were collectively known as "PS/2 interface devices" *long* after the
PS/2 range was essentially forgotten.
--
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