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Memory/circuit problem!!

P

pocketroxetz

Junior Member
Hello, does anyone by any chance know how do this problem I have in my computer design class? Nobody in my class got the problem correct on the test so it was assigned as homework. Can anyone lead me into the right direction at least to approach this?? Thanks!
Here is the scanned problem: Link
 
the msb of the top and bottom decoder inputs are disables that force the one-hot decoder output to the unused pins... that'll tell you the addressing of the ROM and RAM. the middle (I/O) decoder has '000' dangling... same approach.

once you got the addressing mapped the problem is as good as done
 
A15-A0 is used as the common address bus, while A21-A16 is used for selecting the ROM/RAM address space.

For ROM, the ending address is when the 3:8 selects the highest bit, which is 0x0007FFFF. The starting address is when the 3:8 decoder is selected 0, which occurs when A21-A16 =0, so starting address is 0x0000FFFF.

Do the same with RAM and I/O. # of unique I/O locations = size of address space of i/o
 
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