A ROM chip of 4096 x 8 bits has two enable inputs and operates from a 5-volt power supply. How many pins are needed for the integrated-circuit package? Draw a block dia-gram and label all input and output terminals in the ROM.
The Correct Answer and Explanation is:
To determine the number of pins required for the ROM chip and provide a block diagram, let’s analyze the specifications step by step.
Given:
- ROM Size = 4096 × 8 bits
- Two enable inputs
- Operates on a 5V power supply
1. Understanding the ROM:
- 4096 words means 2¹² addresses → requires 12 address lines (A0 to A11).
- 8 bits per word → requires 8 data output lines (D0 to D7).
- 2 enable inputs (typically labeled CE, OE, or CS depending on usage).
- 1 power pin (Vcc) and 1 ground pin (GND).
2. Total Pin Count:
| Signal Type | Count |
|---|---|
| Address Inputs | 12 |
| Data Outputs | 8 |
| Enable Inputs | 2 |
| Power Supply | 1 |
| Ground | 1 |
| Total Pins | 24 |
So, the ROM chip needs 24 pins.
Block Diagram:
+-----------------------+
A0 | |
A1 | |
. | |
. | ROM 4096×8 |
. | |
A11 | |
CE1 | |
CE2 | |
| |
D0 | |
D1 | |
. | |
. | |
D7 | |
| |
Vcc | |
GND | |
+-----------------------+
Explanation (Approx. 300 words):
A Read-Only Memory (ROM) chip with a configuration of 4096 × 8 bits contains 4096 memory locations (or addresses), each storing 8 bits (1 byte) of data. To access one of these 4096 locations, we need to specify its address using binary encoding. Since 212=40962^{12} = 4096, 12 address lines are required (A0 to A11) to uniquely identify each location.
Each location provides 8 bits of output, so there must be 8 data output lines (D0 to D7). These output lines present the contents of the memory location selected by the address lines.
The chip includes two enable inputs (typically labeled CE1 and CE2), which are used to activate the chip. If either enable is not correctly activated (e.g., logic HIGH or LOW depending on the design), the chip remains inactive and does not output data. These inputs are crucial for system-level control, especially when multiple devices share the same data or address bus.
In addition to functional pins, the chip must be powered. Therefore, it requires one Vcc pin (for the 5V power supply) and one GND pin (ground). These are standard for all digital ICs to provide the necessary operating voltage.
Summing up, the ROM chip needs 12 (address) + 8 (data) + 2 (enable) + 1 (Vcc) + 1 (GND) = 24 pins in total. The block diagram illustrates all the inputs and outputs associated with this ROM chip, showing how each signal type connects to the internal memory structure.
