25 Sep
2011
25 Sep
'11
10:56 a.m.
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, there's nothign to stop said chip being programmed to accept a
mouse on the keybaord port and vice versa. It was just never done that
way in the PS/2/.
I do agree that if a machine cna detect it's got the wrong device
conencted, it would have bene better to simply accept that and make use
of it rather than giving an error message.
No, instead, for a decade and a half or so, keyboard
sockets were
coloured green and so were the plugs, and mice in matching purple. (Or
possibly the other way round. I don't use such modern keyboards. :=AC) )
The original IBM ones were all that IBM beige colour.... The colour
coding came later
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.
But finally, in the last few years, you get sockets coloured half
green and half purple, and either a mouse or a keyboard will work in
it - or if the PC has two, either will work in either port.
So they are close enough to be interchangeable - finally. No, that
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.
-tony