Explain the operation of three state bus buffers and show its use in design of common bus.

Three-State Bus Buffers: These are digital circuits that can be in one of three states – high (like logic 1), low (like logic 0), or high-impedance (which means it acts like an open circuit). They’re commonly used in designing bus systems.
Operation:
- When the control input is 1, the buffer is enabled, and the output reflects the input (like a regular buffer).

When the control input is 0, the buffer is disabled, and the output becomes high-impedance, effectively disconnecting it from the circuit.
Designing a Common Bus:
- Imagine you have multiple registers (storage units) in a computer system, and you want them to share a common communication line, or bus.
- To do this, you use three-state buffers. Each buffer corresponds to one register.
- You connect the outputs of all these buffers together to form the bus line.
- Each buffer has a control input that determines whether it’s active (communicating with the bus) or inactive (disconnected from the bus).
- Only one buffer can be active at a time to avoid conflicts.
- You use a decoder to select which register will communicate with the bus at any given time. This decoder takes control signals (like S0, S1, etc.) to choose the appropriate buffer.

Example:
- Let’s say you have four registers, and each register has several bits of data.
- You’d need one set of four buffers for each bit of data (so if each register has 8 bits, you’d need 8 sets of four buffers).
- Each set of four buffers corresponds to one bit from each register.
- The control signals to these buffers come from a decoder, which decides which register’s bit will be on the bus line at any moment.