A ROM is a combinational component for storing data. The data might be a truth table or the data might be the control words for a microprogrammed CPU. A ROM that implements two functions does not require twice the number of gates as a ROM that implements one function. (The decoder is shared by every output function.)

we will design Read only memory using the circuits cloud simulator


if you does not used the circuits-cloud before, you can see this intractable:


Step 1: The ROM Design

Because it is 16*8 ROM, it needs:

- 4 digital inputs

- 8 leds ( as output )

So, drag and drop the components from the digital components panel and connect them

Step 2: Store the Value in ROM Locations

1. Double click in ROM parameter.

2. write an 8-bit value in each location of ROM.

3. click on ( save parameter)

Step 3: Saving and Running the Circuit

save your circuit then running it.

check the output value in each address (location):

if input ( A0, A1, A2, A3 ) =

0000 , output = the value stored in location 0

1000 , output = the value stored in location 1

0100 , output = the value stored in location 2

1100 , output = the value stored in location 3

0010 , output = the value stored in location 4

and so on.

- you can check the circuit:


- also you can see how the circuit works.. in this video

An eight x eight ROM contains 8 words with 8 bits in each word. Addressing 8 locations takes only 3 bits, A0, A1 and A2. Why does your ROM require 4 address bits?
<p>Thank you.</p><p>I already sent them a message via email</p><p>circuitscloud1@gmail.com</p><p>They will fix it , and I will update it as soon as possible.</p>

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