Discussion in 'Electronics Homework Help' started by anonym_nep, Jan 18, 2017.

1. ### anonym_nep

2
0
Jan 18, 2017
Consider a 386 system and it has 40 address lines, calculate the total memory it can address. Design a logic circuit to address three 1024 MB RAMs and two 512 MB RAMs .

2. ### Harald KappModeratorModerator

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Nov 17, 2011
Show us what you've done so far to get at at solution and where you are stuck.

3. ### anonym_nep

2
0
Jan 18, 2017
Consider a 386 system and it has 40 address lines, calculate the total memory it can address. Design a logic circuit to address three 1024 MB RAMs and two 512 MB RAMs .

My attempt is (just giving it a try)

1) Consider a 386 system and it has 40 address lines, calculate the total memory it can address.

=> 2^40 x 4 bytes

2) three 1024 MB RAMs and two 512 MB RAMs

=> one 1024 MB can be addressed by 30 address lines, so three 1024 can be addressed with 32 address lines and for a 512 MB ........stuck from here

Last edited: Jan 18, 2017
4. ### Harald KappModeratorModerator

10,554
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Nov 17, 2011
As the 80386 is a 32 bit system an the address lines addres words (32 bit = 4 byte) this seems correct.

1024 MB requires 30 address lines for bytewise addressing. If the memory were addressed wordwise, not bytewise, then you'd use less address lines. In this contect, 30 seems correct.

No need to get stuck. 512 MB = 1/2 * 1024MB. What does this mean in terms of address lines?

Once you have figured this out, you can proceed to the next part of the task:
The 80386 doesn't know about memory chip sizes. You'll have to devise a way to create chip select signals for the single memory chips from the address lines. Hint: look for address decoder...

Once you have the parts together, it is a good idea to draw a block diagram to show how the components interact. Similar to this example for an 8085 system (you'll need to modify this to a large extend to match the 80386's 32 bit bus and the memory structure required as per the task description above).

5. ### Herschel Peeler

401
65
Feb 21, 2016
Does the memory have to be at ant certain address?
Lower address lines go to the memory's address lines. Higher address lines get decoded to select the memories.
Program memory starts at address 0?
386 interrupt vectors start at 0?

Yes, 386 may have 32 address lines but memory management can add more.