Re: PIC, Keyboard, and USART

On Thu, 23 Mar 2006 21:56:06 GMT, I wrote:

<snip>
What is pin 1 and pin 2? The pins from the connectors? i.e., Data and Clock?
Is that an inverter(buffer I guess)? (i.e. a bidirection link with a
pullup and LP filter?)

As I understand the connector from the schematic (no, I haven't done
keyboard experimentation on my own, so this isn't first hand), the
5-pin round DIN connector has pin 1 as clock and pin 2 as data. 3 is
no-connect, 4 is GND, and 5 is the +5 supply.
<snip>

By the way, I'm not talking about USB keyboards. And I think the PS/2
keyboard connectors (which didn't exist when IBM was putting out that
doc set) are 6-pin, not 5. But the mapping should be findable on the
web. It's probably quite simple. (I have PS/2 to AT connector
adapter plugs that I'm pretty sure just route lines.) It's slightly
possible that the PS/2 keyboards have added to the specifications for
the older DIN 5 connector types, adding more protocols.

The older DIN-5 connector only used 4 conductors. Two power and two
signal. I have a weird USB-looking to PS/2-looking connector adapter
that shows a mouse symbol embossed on the PS/2 end. No idea what it
does, but it looks like it adapts something with a USB connector on it
so that it plugs into a PS/2 mouse adapter hole on a IBM PC/AT system.
So this makes me wonder about USB mice that can actually plug into a
plug normally designed for PS/2 mice. If so, I'm baffled as it seems
to suggest that USB might have been originally designed as an
electrically compatible, but software incompatible, interface. If so,
then it would be possible for a mouse with a USB connector on it to be
plugged into a PS/2 mouse port and to auto-detect which it is talking
with and switch protocols. So now I'm curious about that and
interested in looking much more closely at the USB electrical spec.

Jon
.

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