0. Design using ROM and PLA
EE208: Logic Design
Lecture# 13
Design using ROM and PLA
Prof. Wahied GHARIEB

1. Princess Sumaya University
Digital Logic Design
Read Only Memory (ROM)
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.
Number of words
Size of word

2. Princess Sumaya University
Digital Logic Design
Read Only Memory (ROM)
Memory Size:
102416

3. Princess Sumaya University
Digital Logic Design
Read Only Memory (ROM)
Consider, for example, a 32  8 ROM. The unit consists of 32 words of 8 bits each.

4. Read Only Memory (ROM)

5. Read Only Memory (ROM) Inputs outputs . I4 I3 I2 I1 I0
A7 A6 A5 A4 A3 A2 A1 A0

6. We need a ROM with a size = 8  4
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

7. Read Only Memory (ROM)

8. Read Only Memory (ROM) Types of ROM
1) ROM (masking programming during fabrication for embedded systems). Computer BIOS, washing machine, …etc
2) PROM (Programmed using special device used by user). Low cost one time programming (OTP) chip
3) EPROM (Erasable using ultraviolet light for a given period of time and then can be reprogrammed)
4) E2PROM (Electrically erasable like flash memory). It can be used for microcontroller developments

9. Programmable Logic Devices

10. Programmable Logic Devices

11. Programmable Logic Array (PLA)
F1=AB\+AC+A\BC\
F2=(AC+BC)\

12. Example 7.2 :Implement the following two Boolean functions with a PLA:
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\
F2= AB+AC+A\B\C\
F1= (AB+AC+BC)\
F2= (A\B+A\C+AB\C\)\

13. Programmable Logic Array
F1= (AB+AC+BC)\
F2= AB+AC+A\B\C\ AB AC BC
A\B\C\