time for refreshing memory

[nancy_n]

suppose having 256 rows in a microcomputer memory and we need to refresh them. each row must be refreshed at least once every 4 ms (refreshing occurs at periodic basis).what is the time period between successive requests??
i know the max period which is 4 ms, but how should i know the time period if all i am given is the above.????
plus, how can we know for how long a refresh address counter is needed??

[saphalline]

I would think, given the simplistic nature of the question, it would be a straight shot of 4 ms times 256 rows = 1.024 s.

Your second question seems to be the result of an over-analysis! If that was all the info you were given, you don't need to know any more!

[nancy_n]

the time period between successive refresh requests is a maximum of 4 ms. isn t there a formula or any inf. that can be retreived given that the memory is a 64K * 1 DRAM ???
the second question would have as an answer 1.024 s as u replied earlier. but this answer would be obtained when refreshing once every 4 ms. which is only a hint, we can have more than 1 refresh in 4 ms.
can't we know the exact result??? thank u

[saphalline]

What is the nature of these questions?

Yes, there will be a "formula" for determining the exact values needed for any given device. But I was not aware of any specific device being named here. If there is a specific device in question, then what is the part number? The specs for any chip are widely available online. Do you have a DRAM chip for which you are trying to program in a micro-controller setting?