Question 10569 – Digital-Logic-Design

1) RAM is not a combinational circuit. For RAM, the input is the memory location selector and operation (read or write) and another byte (which can be input for write operation or output for read operation), and the output is either a success indicator (for write operation) or the byte at the selected location (for read operation). It does depend on past inputs, or rather, on the past write operations at the selected byte. This is a sequential logic circuit.
2) PLA is a combination circuit as ROM. PLA is a programmable AND array and a programmable OR array. A PLA with n inputs has fewer than 2n AND gates (otherwise there would be no advantage over a ROM implementation of the same size). A PLA only needs to have enough AND gates to decode as many unique terms as there are in the functions it will implement it.