Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
Excellent - thanks Paul.
"Paul" <nospam@needed.com> wrote in message
news:nospam-0306041818500001@192.168.1.177...
> In article <c9n01h$ksq$1@news6.svr.pol.co.uk>, "xyz" <dont@spamme.com>
wrote:
>
> > When you enable the game port in the BIOS, you are confronted with
several
> > configuration options e.g. 200/300. 200/330 etc. What do these numbers
> > relate to. 200/300 is working for me, but I'm just curious.
> >
> > Cheers in advance.
>
> They are called I/O addresses and every device that uses them
> should have a unique value. The reason you have more than
> one option, is for resource juggling - if another device
> has a fixed allocation, devices that have multiple values can
> be configured to use a non-conflicting value.
>
> As for the concept of I/O, everything these days is memory
> mapped. That means the processor address bus is decoded by
> hardware logic, to identify just the particular register
> in a device you are after. IOW, the hardware looks like
> a chunk of ram, and the processor doesn't do anything
> different when accessing DRAM, as opposed to some chip
> register. They are all accessed with load or store
> instructions.
>
> Even today, a processor with an Intel instruction set has
> to support I/O instructions. The "IN" and "OUT" instructions
> are examples of I/O instructions. Think of this as a legacy
> way for the processor to read/write the hardware.
>
>
http://faydoc.tripod.com/cpu/in.htm
>
http://faydoc.tripod.com/cpu/out.htm
>
> Looking at a Z80 family datasheet, an I/O instruction
> almost looks like a load/store, except that the IORQ
> signal gets asserted during the bus transaction. I guess
> that makes the IORQ into a 33rd address bit. The timing
> on the bus is also different, because the design intent
> was to access hardware devices that don't perform the
> same way as a memory.
>
> I wish I could remember more about this, but as I've
> thrown out all the docs I had on this stuff, it is hard
> to look up, and also hard to find the old info on the
> web. The information predates PDF versions or Postscript
> versions of documents, and many times the books were
> only printed and not in an electronic form.
>
> HTH,
> Paul
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