# RAM memory diagram using decoders

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1. Feb 8, 2017

### gruba

1. The problem statement, all variables and given/known data
Draw a block diagram of $32kx8 bit$ RAM memory using decoders $DEC 3/8$ and memory components $8kx8 bit$.

2. The attempt at a solution
First we find the number of memory components:
$$N=\frac{32kx8}{8kx8}=\frac{2^{18}}{2^{16}}=4$$.

The number of decoders is
$$32/8+1=5$$

There are 4 blocks of memory so the decoder needs to decode 2 address lines to 4 select lines (these are connections between memory elements and four decoders (see attachment)).

Is this diagram correct?

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2. Feb 12, 2017

### Baluncore

You have made it too complex. Why do you think the number of decoders is 32/8 + 1 = 5 ?

DEC3/8 means 3 binary input lines with 8 outputs. Note that 2^3 = 8. But only one of those 8 outputs will be active at the time.
You will have 4 memory blocks. Which positions will they map to? 0, 1, 2 and 3 ? or somewhere else, maybe 4, 5, 6 or 7 ?