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Old 12-14-2009, 02:10 AM   #1
shilpa rangappa
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memory mapped i/o and i/o mapped i/o

Hi All,

Can anyone explain me..
what is memory mapped i/o and i/o mapped i/o?
And also difference between the two...

Old 12-14-2009, 11:27 PM   #2
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Many CPUs are better at addressing "memory" than they are at addressing "I/O Ports." There are just more and more-flexible instructions available for memory access.

So, hardware designers build their cards to recognize "read" and "write" requests to certain memory-addresses as being directed to certain hardware-latches on their cards. That is, when you "read address $XYZ," you get the contents of a particular hardware circuit. Likewise, a "write" sets the values of a bank of certain switches.

The operating system arranges for those memory addresses to be protected such that only the kernel can read and/or write to them.

The practice is so widespread and so useful that some microprocessor designs don't even have I/O-port instructions. The designers judged that they simply didn't need them.


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