Designing a Programmable Read-only memory (PROM).

Introduction:

Programmable Read-Only Memory (PROM) is a crucial component in digital circuit design,VLSI and embedded systems, allowing users to customize memory content according to their specific needs. This article outlines key steps to design a Programmable Read-Only Memory.

PROM is a type of non-volatile memory that stores data permanently. Unlike Random-Access Memory (RAM), PROM retains information even when power is turned off.

Its programmability allows users to write data to the memory only once, making it an ideal choice for applications requiring fixed but customizable data storage.

Choosing PROM Type:

PROMs come in different types, such as Fuse PROM (FPROM) and One-Time Programmable (OTP) PROM. Select the type based on your application's requirements.

Memory size Definition and calculation :

Determine the size of the PROM needed for your specific data storage requirements. Consider the amount of information to be stored and any future scalability needs.

To calculate memory size

use 2^x * y = memory size

Where x = number of input and

y = number of output

For example:

If x = 8 and y = 4

PROM size = 2^8 * 4 = 1024bits or 128bytes.

Architecture of PROM:

PROM architecture is basically made up of

A fixed AND array(or decoder) and Programmable OR array.

Design:

To design a PROM carefully follow the steps.

1. Identify the number of bits of input and output data required

2. Identify the operation required to get output from input.

3. Make a truth table for both input and output data using the operation identified in step2

4. Implement the input data using the suitable decoder (e.g for 2 bit input use 2x4 decoder)

5. Using the data from the output section of the truth table . Do the OR operation using an OR array accordingly.

Following the output from the OR array, Cheers! you have just designed a PROM for your data/information.