piclist 2002\08\19\150658a >
Thread: More advanced system design..
face BY : Jim email (remove spam text)

  "I really don't see any advantage to a
   separate I/O map over use of memory
   mapped I/O."

Simple "byte" I/O, perhaps not.

But consider that a separate I/O instruction actually
translates (maps), in effect, an address to "hardware"
via an additional processor output pin that in effect
"decodes" those I/O instructions and therefore does not
require the designer to provide additional hardware to
decode an address from memory space - for a small
system it saves hardware decode logic that would
otherwise be required ...

Such direct connection "support" IC's such as the Z80
SIO, PIO, CTC chips were I/O devices that were addressed
via I/O instructions, all these are all capable of
interrupting and supplying the lower portion of an
interrupt service address during interrupt service ...
through the use of an "I/O" instruction no additional
address decode off the address bus is required.

RF Jim

{Original Message removed}
<005501c247b3$97207500$0100a8c0@piii500a> 7bit

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