Question

help needed for logical design
ROM is actually a memory part.it should come under sequential circuit where memory is an element....instead it comes under combiantional circuit howz this possible?

Answer 1

ROM is actually a pre-programmed memory. You just need to supply an address - it will immediately respond with an answer. There is no requirement of clocking to do this. You don't have clocked operations like bit latching in ROM.

In sequential systems, the clocking is done to operate these latches. Without this operation, ROM is just a combinational system. And unlike a sequential memory, ROM is incapable of recording a value from one clock cycle and releasing the value in another clock cycle.

Answer 2

thanks that realy helped me
den wat is the concept behind EEPROM and EPROM

Answer 3

EEPROM and EPROM are just like ROMs - you just supply an address and get back a reply - no clocks included!

The only difference is that it is possible for the designer to program it. The circuit on its own is still unable to use it as a latchable memory. Vanilla ROMs on the other hand, can be programmed only by the manufacturer at a factory.