Re: How PC parallel port Is connected internally?

On 28 Jun 2005 01:55:13 -0700, "Ali" <abdulrazaq@xxxxxxxxx> wrote:

>Humm.. Great text! Well Jon thanks for your contribution , i would
>appreciate if you can see us discussing the same issue from different
>prospective.
>[http://groups-beta.google.com/group/microsoft.public.development.device.drivers/browse_frm/thread/50869515be02a63f/9fe6f1d60ae47fa4#9fe6f1d60ae47fa4]
>See Tim's latest post for more understanding.

Thanks. I've looked. I believe I have a full IEEE 1284 specification
laying around, somewhere. I didn't remember about it until I saw some
diagrams on the web on the subject, then it all came flooding back to
me. You will definitely want that spec handy. The Microsoft doc is
helpful _after_ you know what is in it, since that doc doesn't exactly
tell you how these things are precisely transferred to the PnP under
Windows.

However... my vague memory also recollects that you have a number of
device layers under NT. 64? Something like that. Only one of them
is the one that directly manages the hardware I/O, if memory serves.
Since Windows is _already_ going to have something hooked in at that
level in order to facilitate the very communications initially
required to participate in the PnP recognition of your external
device, it will be that driver that talks to the actual I/O ports on
the machine in question. Your driver (or, at least, one part of your
driver) will get loaded in at a higher level. Much as the printer
drivers are. I don't think they normally are allowed to completely
replace the bottom level I/O driver. If you did replace that lowest
level, wouldn't that mean your driver would also have to support the
PnP signaling under IEEE 1284 needed to recognize the removal of your
device and its replacement by yet another device? And if it didn't
need to do so, under the possibility that this is handled at a
slightly "higher" level driver, wouldn't that mean there is no real
need for you to intercede at this then very low level?

Just thinking out loud...

Jon
.

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