On 24 September 2011 18:36, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Exactly (but for the connector) does the PC/AT
interface differ from
the PS/2 interface?
The connector is a rather important part of the deal. The "standard",
I disagree. The conector is a part of the standard, but hardly an
important one.
If the signals are the same (as they are on a PC/AT and PS/2 keyboard
interface), then changing the connector is a 5 minute job with a
soldering iron. If the signal protocol is different, then most likely
I'll have to write new firmware of the microcontroller in the keybaord,
after first reverse-engineering the wiring of the keyswitch matrix, etc.
Which do you think is easier?
I would not be able to do either so it's entirely academic to me.
Firstly, I am suprised you couldn't solder 4 wires onto 4 pins of a DIN
plug. When I was a lad, audio equipment often came with a few unconnected
plugs in the box, an they expected you to solder up the right
interconnecitng cables. How times change...
Secondly, I know very little about medical matters. But I am sure that an
operation to removen ingrowing toenail is a lot simpler than a kidney
transplant (say). And however little electronics yuo know, I am sure you
can judge which of the following 2 procedures is more complicated :
1) Cut off an existing plug, strip the cable, solder 4 wires ot the pins
of a new plug
2) Dismantle a keyboard, trace out how it's wired (so that you know that
hte 'Q' key links column 5 to row 2 or whatever), write a program for the
appropraite microcroller to read that pattern of keys and talk the
appropraite protocol to the host machine, then burn that program into a
microcontroller, desolder the existing microcontroller from the keyboard
PCB and solder in the one you've just programmed.
Nor would I butcher a keyboard like that - I'd just go and get an
appropriate one from the bits pile.
Not everybody has a 'bits pile' of PC parts... And you might want to use
a particular keyboard because you like the feel (as in the type M that
started this thread). If your type M has the wrong cable, you either have
to track down the right cable, use a differnet keyboard that doesn't feel
as nice, or change the plug. For me, the answer is obvious.
The point is that PS/2 keyboards were not necessarily
attached to
PS/2s. They became an extremely widespread industry standard, even
beyond PC compatibles - e.g. later Acorn ARM RISC machines such as the
RiscPC and A4000 and A7000 used them, too, as did some PReP Mac
clones.
Sure. But PC/AT keyboards (with the larger 5 pin DIN plug) were not
restricted to PC/AT machines only either. I have an X-terminal that uses
one. I think some Whitechapel workstations did too (the Hitec series)
Until USB came along, most computer keyboards from the
start of the
1990s on, for 15-odd years, were PS/2 keyboards. The name no longer
had anything at all to do with IBM PS/2 computers and continued long
True enough. But surely you accept that the name came from the IBM PS/2
machines.
It's not about the computer being used. It's
not about the connector,
which was used for other things too, I'm sure. It's not about the
protocol, as that was used for other devices with a
physically-incompatible connector. It was the /combination/ of the 2
protocols (K/b and mouse) and the single shared connector. That's what
a PS/2 interface meant.
Are you now claiming that a PS/2 interface has to support both a keyboard
and a mouse (one a pair of conencotrs, or by a Y cable, or something)?
Becuase I am sure there are counterexamples to that.
To me, a PS/2 keyboard is fitted with a 6 pin Mini-DIN connector, 4 pins
are actualyl used (ground, +5V, clock, data), and it talks the protocol
described in the appropriate IBM Technical Reference manual. Ditto a PS/2
mouse.
A PC/At keybaord has a 5 pin DIN connector, but the signal protocol is
the same as the one for a PS/2 keybaord. This means you can convert on
into the other by just changin the connector.
I think I'll trust IBM's technical documentation above Wikipedia...
-tony