Read Only Memory (ROM)

Number of words

Size of word

• A block diagram of a ROM consisting of k inputs and n outputs is shown below.

The inputs provide the address for memory, and the outputs give the data bits of the stored word that is selected by the address.

The number of words in a ROM is determined from the fact that k address input lines are needed to specify 2k words.

Read Only Memory (ROM)

Memory Size:

102416

Read Only Memory (ROM)Draw a 32 8 ROM. The unit consists of 32 words of 8 bits each.

Read Only Memory (ROM)

Read Only Memory (ROM) Inputs outputs .

I4 I3 I2 I1 I0 A7 A6 A5 A4 A3 A2 A1 A0

1 0 1 1 0 1 1 00 0 0 0 0

Read Only Memory (ROM)Example 7.1: Design a combinational circuit using a ROM. The circuit accepts a three-bit number and outputs a binary number equal to the square of the input number. (minimize the ROM if possible)

Read Only Memory (ROM)Example 7.1: Design a combinational circuit using a ROM. The circuit accepts a three-bit number and outputs a binary number equal to the square of the input number.

We need a ROM with a size = 8 4

Read Only Memory (ROM)

Programmable Logic Devices

FPGAs are programmable digital logic chips. What that means is that you can program them to do almost any digital function.

Here's the general workflow when working with FPGAs:

You use a computer to describe a "logic function" that you want. You might draw a schematic, or create a text file describing the function, doesn't matter.

You compile the "logic function" on your computer, using a software provided by the FPGA vendor. That creates a binary file that can be downloaded into the FPGA.

You connect a cable from your computer to the FPGA, and download the binary file to the FPGA.

That's it! Your FPGA behaves according to your "logic function".

Keep in mind that

You can download FPGAs as many time as you want - no limit - with different functionalities every time if you want. If you make a mistake in your design, just fix your "logic function", re-compile and re-download it. No PCB, solder or component to change.

The designs can run much faster than if you were to design a board with discrete components, since everything runs within the FPGA, on its silicon die.

FPGAs lose their functionality when the power goes away (like RAM in a computer that loses its content). You have to re-download them when power goes back up to restore the functionality.

Programmable Logic Array (PLA)

F1=AB\+AC+A\BC\

F2=(AC+BC)\

Programmable Logic Array (PLA)

Example 7.2 :Implement the following two Boolean functions with a PLA:

F1(A, B, C) = (0,1,2,4)

F2(A, B, C) = (0,5,6,7)

F1 F2

F1= A\B\+A\C\+B\C\

F1= (AB+AC+BC)\

F2= AB+AC+A\B\C\

F2= (A\B+A\C+AB\C\)\

Programmable Logic Array

F1= (AB+AC+BC)\

F2= AB+AC+A\B\C\