FSM implementation

Question 1

How do we implement the Next State Logic part of an FSM?

Answer 1

We create a current-state | next-state table

We create Boolean expressions for each state bit using Karnaugh maps

We use these expressions to create a logic circuit

This connects to the state register

Question 2

How do we implement the state register part of an FSM?

Answer 2

We use D flip-flops for each state bit

Question 3

How can we use a ROM to implement next-state logic?

Answer 3

We can map each current_state codeword to the ROM address

At each address we store the relevant next_state codeword.

The next state is then found with a simple lookup of the current state

Question 4

What is the third state in tristate and when do we use it?

Answer 4

Z

High Impedence state

When one device is sending information over a bus, all other transmitting devices should be disconnected. This is achieved by putting output stage of devices into a high impedance state, Z, that effectively disconnects the gate from the output wire