Q6Digital Electronics
Question
4 marks
Write short notes on the following: (i) Sequential Memory (ii) ROM as a PLD
Answer
Sequential memory accesses data in a fixed order, unlike random access; ROM can be used as a PLD by programming the AND plane (decoder) outputs into the OR plane.
- Examples: magnetic tape, FIFO buffers, shift registers used as delay lines
- Access time depends on position of the data relative to current read position
- Used in streaming, buffering, pipeline stages
- The AND plane (address decoder) generates all 2^n minterms - this is fixed
- The OR plane (data array) is programmable: set each bit to include or exclude a minterm
- A ROM with n inputs and m outputs can simultaneously implement m Boolean functions each of up to n variables
- Disadvantage: ROM is inefficient for sparse functions since all 2^n minterms are always decoded