How a multiplexer can be used as ROM? Explain in brief.
Q.) How a multiplexer can be used as ROM? Explain in brief.
Subject: Digital SystemsA multiplexer (MUX) can be used as a Read-Only Memory (ROM) by using the data select lines as address lines and the inputs as data lines. The output of the MUX will be the data stored at the address specified by the data select lines.
Here's a step-by-step approach to explain how a multiplexer can be used as a ROM:
Data Select Lines as Address Lines: In a multiplexer, the data select lines are used to select which input to pass to the output. When using a MUX as a ROM, these data select lines become the address lines. The number of address lines determines the number of memory locations in the ROM. For example, a 2-to-1 MUX has 1 select line, which can be used as an address line to access 2 (2^1) memory locations.
Inputs as Data Lines: The inputs of the MUX are used as data lines when the MUX is used as a ROM. The data stored at each memory location is determined by the state of the corresponding input line when the ROM is programmed. For example, in a 2-to-1 MUX used as a ROM, if the input line corresponding to address 0 is high and the input line corresponding to address 1 is low, then the ROM stores a 1 at address 0 and a 0 at address 1.
Output as Data Output: The output of the MUX is the data output of the ROM. The data stored at the address specified by the address lines is passed to the output.
Programming the ROM: The ROM is programmed by setting the state of the input lines (data lines) for each possible value of the address lines. This is typically done at the time of manufacturing.
Here is a table showing how a 2-to-1 MUX can be used as a ROM:
| Address (Select Line) | Data Input (Input Lines) | Data Output (Output) |
|---|---|---|
| 0 | 1 | 1 |
| 1 | 0 | 0 |
In this example, the ROM stores a 1 at address 0 and a 0 at address 1. When the address line is 0, the output is 1, and when the address line is 1, the output is 0.
It's important to note that while a MUX can be used as a ROM, it's not a practical solution for large amounts of memory because the number of input lines (and hence the amount of data that can be stored) increases exponentially with the number of address lines. For example, a 4-to-1 MUX has 2 address lines and can store 4 bits of data, but a 16-to-1 MUX has 4 address lines and can store 16 bits of data.