Example - Answering Machine

Verbal description:

• On the third ring, answer the phone, play a greeting, and record a message.
• After recording a message, hang up.
• If a telephone is taken off hook within three rings, do nothing.

State transition diagram:

States = {idle, count1, count2, play greeting, recording}
Inputs = {ring, offhook, end greeting, end message, absent}
Outputs = {answer, record, recorded, absent}

Trajectory example

Suppose input sequence is

ring, ring, ring, end greeting , end message, …

State response:

idle, count1, count2, play greeting, recording , …

Output sequence:

absent, absent, answer, record, recorded, …