Re: PIC, Keyboard, and USART


"Jonathan Kirwan" <jkirwan@xxxxxxxxxxxxxx> wrote in message
news:7r6622pdhbv09b2qob88tf99j3l4k0uke8@xxxxxxxxxx
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.


yeah, the USB uses a HID protocol for keyboards.... something entirely
different I guess. I've downloaded the specs but haven't been over them yet.

The 5 and 6 pin connectors are compatible but the order is different. The
web site I have gave me the order but I'm not sure if it corresponds to what
you have.

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.


Could it be possible that there is some translation circuitry inside the
connector? There is a difference in being that the USB uses a differential
pair for data transmission so its not possible for a rewiring?

Jon

Thanks,
Jon


.

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