A RAM chip has a capacity of 1024 words of 8 bits each (1K × 8) . The number of 2 × 4 decoders with enable line needed to construct a 16K × 16 RAM from 1K × 8 RAM is
A. 4
B. 5
C. 6
D. 7
Answer : (B)
Explanation :
Basic RAM chip size = 1K × 8
RAM to construct = 16K × 16
For each word in the new RAM, word size is 16 bits, So you need to put 2 RAMs (1K × 8) to create (1K × 16).We can put such 16 dual RAMs to create 16K × 16.i.e., 16 X (1K × 16).
To address 16K locations in 16K × 16 we need 14 bits. 10 bits will be used to to locate the word in 1K × 16 locations. Rest of the 4 bits will need to be used to identify one of the 16 locations. For this we will need 4×16 DECODER.
But we need to solve this problem with 2×4 decoders. You can arrange (or will need) 5 such 2×4 decoders to use 4×16 decoder.
Hence we need 5 2×4 decoders. Answer: B.
Topics to revisit :
Decoders
Encoders
Multiplexers
DeMultiplexers
References :
A. 4
B. 5
C. 6
D. 7
Answer : (B)
Explanation :
Basic RAM chip size = 1K × 8
RAM to construct = 16K × 16
For each word in the new RAM, word size is 16 bits, So you need to put 2 RAMs (1K × 8) to create (1K × 16).We can put such 16 dual RAMs to create 16K × 16.i.e., 16 X (1K × 16).
To address 16K locations in 16K × 16 we need 14 bits. 10 bits will be used to to locate the word in 1K × 16 locations. Rest of the 4 bits will need to be used to identify one of the 16 locations. For this we will need 4×16 DECODER.
But we need to solve this problem with 2×4 decoders. You can arrange (or will need) 5 such 2×4 decoders to use 4×16 decoder.
Hence we need 5 2×4 decoders. Answer: B.
Topics to revisit :
Decoders
Encoders
Multiplexers
DeMultiplexers
References :
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