In the case where the Control Program (Control) is sending data to the Swipe-Card Reader (Swipe), we
have the following steps:
- Control sends to Swipe.
- Swipe replies with "OK, event primed."
- A big delay occurs until the next person swipes their card.
- Swipe uses a pulse to say "I have data available."
- Control sends a message, "What is your data?"
- Swipe replies with "Swipe card ID # xxxx was swiped."
- Control sends message, "Change LED to GREEN."
- Swipe replies with "OK."
- A 20-second delay occurs, while the door is opened.
- Control sends message, "Change LED to RED."
- Swipe replies with "OK."
In this case, there was one pulse, and three messages.
Granted, you would prime the event just once, so the first message can be eliminated.