Dead States-The Purgatory of state Machine Dead States-The Purgatory of state Machines State machines with encoded state bits don' t always use all possible states. For example, if you have a 20-state state machine, you would use a five-bit state register. This would leave 12 unused state values. Since states are usually counted incrementally from zero, our example would look like this States What The States are Used For Normal operation 20-31 Not used: these are"dead"states If the state machine ever enters a state 20-31, errors are likely; worse, the machine may lock up totally, with the state machine forever in one of these ille- gal states. It may require a hard reset to recover from this condition Clearly, it,'s best to ensure your state machine never reaches a dead state. How ever, a robust design will at a minimum ensure that if the state machine does enter a dead state, it will exit the dead state immediately and then perhaps enter a quiescent state The Ten Commandments of Excellent DesignDead States—The Purgatory of State Machines 8 The Ten Commandments of Excellent Design Dead States—The Purgatory of State Machines State machines with encoded state bits don’t always use all possible states. For example, if you have a 20-state state machine, you would use a five-bit state register. This would leave 12 unused state values. Since states are usually counted incrementally from zero, our example would look like this: If the state machine ever enters a state 20-31, errors are likely; worse, the machine may lock up totally, with the state machine forever in one of these ille￾gal states. It may require a hard reset to recover from this condition. Clearly, it’s best to ensure your state machine never reaches a dead state. How￾ever, a robust design will at a minimum ensure that if the state machine does enter a dead state, it will exit the dead state immediately and then perhaps enter a quiescent state. States What The States are Used For 0-19 Normal operation. 20-31 Not used: these are “dead” states