Memory Mapped IO

Question

Plz solve

Consider the hypothetical processor which supports  $512k$ words memory.It uses the memory mapped input output configuration. In which when $2MSB$ bits of address are $1$ then assigned to input output port. How many number of input output port address and memory address are possible in the processor respectively?

Comments

http://www.ques10.com/p/8750/explain-in-brief-memory-mapped-io-2/

in the above link is is written that

 I/O and memory, both in combination are treated as memory.  

so by considering this

                   : I/O addresses = 1 * 2¹⁷ 

                    :Memory addresses  = 4 * 2¹⁷

please help someone about Memory mapped I/O and I/O mapped I/O concept.

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 I/O and memory, both in combination are treated as memory.

This means, there is one memory and we will cut down the memory as two parts: one part would be memory related instructions and second part would be I/O related instructions

Int the above questions, they are saying that there are 2¹⁹  words memory and in these 19 bits, 2 bits(11) are used for I/O related devices means 1*2¹⁷ addresses related to I/O and there are 3 other combinations remaining(00.01,10), hence 3*2¹⁷ addressees related to memory

Answer 1

Number of memory words can be addressed = 2¹⁹.

19 bits to address a word.

Given that when MSB's are 11, then the address corresponds to I/O.

Using, 2 bits, 4 combinations are possible.

We give "11" to I/O and "00,10,01" to memory address.

So, I/O addresses = 1 * 2¹⁷

Memory addresses = (4-1) * 2¹⁷ = 3 * 2¹⁷

Comments

"Given that when MSB's are 11, then the address corresponds to I/O."

Cannot understand this portion

elaborate plz :)
 

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From the question,

When 2 MSB bits of address are 1 then assigned to input output port

It means, if the two MSB's in a 19 bit address are 1 and 1, then the address is assigned to I/O